Full Stack Developer (Core Builder) — Startup

About Bitrefill
Bitrefill is the world's leading crypto lifestyle platform. We enable millions of users globally to pay for gift cards, mobile phone refills, and everyday goods using Bitcoin, Lightning Network, and other digital assets. Our long-term goal is to provide everyone with the tools to use crypto as real "digital money" daily — without needing to register for additional services or log into a web platform.
We are now actively building a new product: the Bitrefill crypto card for paying for goods and services in everyday life.
The Role
We are looking for a Senior DS/ML Engineer to help us make data-driven decisions across fraud detection, Lightning Network liquidity optimization, user behavior modeling, and risk scoring for the crypto card.
You won't just build models — you'll help shape the ML infrastructure of a fast-growing crypto-payments startup.
What You'll Do
Fraud & Risk ML — Develop anomaly detection models, transaction scoring for withdrawals, and real-time predictive rules to flag suspicious activity.
Lightning Network optimization — Build models to optimize payment routing, channel liquidity management, and predict channel health.
Crypto card infrastructure — Create credit risk models and user scoring for card issuance without traditional credit history.
LTV & churn prediction — Forecast user behavior to improve retention and conversion, especially in low-crypto-adoption countries.
Product & growth analytics — Develop ML-driven hypotheses for A/B testing and recommendation systems (e.g., which gift cards to offer).
Data pipeline & MLOps — Help build pipelines for training and deploying models to production (alongside engineers).
Requirements
5+ years of experience in Data Science / Machine Learning, ideally in fintech, payments, crypto, or high-throughput transactional systems.
Strong experience building anti-fraud models, time series forecasting (for transactions), LTV predictions, or classification/clustering models.
Python — solid proficiency (pandas, scikit-learn, xgboost/lightgbm; PyTorch/TensorFlow is a plus).
SQL — advanced level.
Experience with Airflow, dbt, or similar ETL/ML pipeline tools.
Understanding of Lightning Network basics (or strong willingness to dive deep within 1–2 weeks).
English — sufficient to discuss ML metrics and business problems fluently.
Big Pluses
Experience with graph models (Node2Vec, GNNs) for transaction chain detection.
Familiarity with blockchain analytics (on-chain data, addresses, transactions).
Experience in credit scoring without traditional credit history.
MLOps skills (Docker, Kubeflow, MLflow, or at least deploying models via FastAPI).
Personal experience using Bitrefill or crypto as a payment tool.
We Offer
Fully remote work from anywhere in the world (with ~4–6 hours overlap with Stockholm time zone).
Opportunity to build an ML system from scratch in a startup that is truly changing how people use crypto.
Competitive salary + equity (tokens) or profit-sharing.
Minimal bureaucracy — maximum responsibility and freedom.
Work with cutting-edge technologies: Lightning Network and crypto cards.
How to Apply
Send your resume and a link to your GitHub / Kaggle / project where you solved a fraud, time series, or risk modeling problem. Mention if you have experience with Lightning or blockchain analytics — if not, just tell us how quickly you can learn new domains.

We are supporting a well-funded startup building a next-generation blockchain gaming platform powered by AI technology. The company is backed by strong investors and has already launched an initial version of its product. As the platform evolves, the team is rebuilding its technology stack and infrastructure to support scalable on-chain gaming mechanics, digital asset ownership, and advanced blockchain integrations. This role goes far beyond a typical executive position. The client is looking for a Chief Technology Officer (CTO) with deep blockchain expertise and strong leadership capabilities who can define the long-term technical vision, lead engineering execution, and help shape the future direction of the company. The ideal candidate has a hands-on mindset, startup experience, and is passionate about building innovative products in the blockchain gaming space. Responsibilities Define and lead the company’s overall technical vision and engineering strategy Oversee architecture and development of blockchain infrastructure and gaming systemsLead and scale engineering teams across Web3, backend, frontend, DevOps, and AI functions Drive technical decision-making for scalability, security, and product performance Collaborate closely with founders, product teams, and stakeholders on roadmap execution Establish engineering processes, development standards, and technical best practices Guide smart contract architecture and blockchain integrations Support hiring, mentoring, and team growth across technical departments Evaluate emerging technologies and industry trends relevant to blockchain gaming and AIRequirements Strong leadership experience as a CTO, Head of Engineering, or senior technical leader Deep understanding of blockchain ecosystems, Web3 technologies, and smart contractsStrong technical background in modern software development and system architectureExperience managing and scaling engineering teams in startup environments Understanding of cloud infrastructure, DevOps, and scalable distributed systems Experience with React, Node.js, or modern web technologies is a strong plusFamiliarity with gaming, NFT ecosystems, or digital asset platforms is highly preferredStrong communication and decision-making skillsEntrepreneurial mindset with interest in long-term product ownership and company growth Benefits and PerksCompetitive executive compensation package with equity participationHealth, dental, and vision coverage Unlimited PTOPension contributionRemote-friendly environment with flexibilityExpense reimbursement for home internet and phoneOngoing professional development and leadership growth opportunitiesOpportunity to shape the future of a blockchain gaming platform at an early stage Hiring Process Introductory conversationStrategic and technical discussions with leadership teamFinal alignment and offer discussions

Hello everyone,
We have a website where we organize paid raffles/giveaways. We are looking for teammates who have marketing knowledge or an audience/communit and can attract people to join these raffles.
Once the required number of participants is reached, the raffle will be drawn, and after the prizes are distributed, you will receive 15% of the remaining profit from the website. I would also like to point out that your earnings are determined as soon as a raffle is created.
Requirements:
-Someone who already has an audience/community and can encourage them to participate in paid raffles,
-Someone who owns a YouTube channel, Telegram channel, or groups on other platforms and can promote/share the raffles. Or instead of the points above, someone with strong marketing skills
-Who can attract users to the website using their own methods.
Additional notes:
Payments will be made to you via Laborx once the total participant count is completed. Raffles can be for 1,000 people or even 1 million people. The more participants you bring, the better.
More games and features will also be added to the website to keep users active on the platform. If you would like to join us on this highly profitable journey, please don't hesitate to get in touch. 
Note; The website is already live and fully operational. We are about to launch our very first raffle.

Worklo is building the future of professional services automation — combining our core PSA platform with a blockchain-powered salary distribution system that automates compensation directly from project data, time entries, role assignments, and milestones. This role is for a highly capable engineer who can own both traditional full-stack SaaS development and blockchain infrastructure, designing and scaling an end-to-end system that bridges Worklo’s platform with secure on-chain payroll execution.You’ll be one of the core engineers shaping both Worklo PSA and our blockchain payroll architecture. This is a greenfield, high-ownership opportunity where you’ll make major architectural decisions across smart contracts, backend systems, frontend applications, database security, and blockchain integrations.ResponsibilitiesFull Stack Platform DevelopmentOwn full product features end-to-end: database schema design, backend API development, frontend UI implementation, deployment, and monitoringBuild and maintain scalable applications using Next.js 15 (App Router, React Server Components), TypeScript, Express.js REST APIs, and SupabaseDesign and implement PostgreSQL schemas, optimize queries, and maintain database performanceWrite and maintain Supabase Row Level Security (RLS) policies for secure multi-tenant data isolationBuild polished, reusable UI components using React, shadcn/ui, and Tailwind CSS 4Develop secure REST APIs with proper validation (Zod), authentication, and error handlingIntegrate third-party services including SMTP, file storage, analytics dashboards, and workflow toolsDebug production issues, improve observability, and contribute to architecture decisionsBlockchain System DevelopmentDesign and implement Solidity smart contracts for salary calculation and automated payroll distributionBuild compensation logic covering:Hours workedRole multipliersMilestone bonusesStablecoin payouts (USDC/USDT)Deploy and manage smart contracts on Polygon L2 or similar EVM-compatible networksDevelop backend blockchain integrations that sync Worklo’s Supabase data with on-chain payroll systemsBuild wallet registry systems enabling MetaMask and WalletConnect integrationImplement blockchain event listeners, webhooks, and indexing systems to synchronize off-chain and on-chain statesCreate secure transaction signing, key management, and server-side blockchain interaction layersBuild in-app dashboards for payroll visibility, wallet management, and transaction historyWrite and maintain comprehensive test suites for smart contracts using Hardhat, Foundry, or similar frameworksOptimize contracts for gas efficiency, security, and upgradeabilityRequirements3+ years of professional experience in full-stack software development3+ years of blockchain development with production-deployed smart contractsStrong TypeScript/Node.js expertise across frontend and backend systemsStrong Solidity skills, including:Reentrancy protectionAccess controlUpgradeability patternsGas optimizationDeep experience with React and modern frontend architectureSolid understanding of PostgreSQL, database design, indexing, and optimizationExperience with Supabase, Firebase, or similar backend platformsExperience designing secure REST APIs and authentication systemsFamiliarity with ethers.js, viem, or similar blockchain interaction librariesExperience with Polygon or other EVM-compatible L2 ecosystemsStrong understanding of ERC-20 standards, stablecoin mechanics, and wallet integrationsAbility to work independently in a remote-first, async environmentComfortable making technical decisions with real product ownershipNice to HaveExperience with Next.js App Router and React Server ComponentsHardhat, Foundry, Truffle, or OpenZeppelin expertiseDeFi protocol or on-chain financial system experienceFamiliarity with The Graph or blockchain indexing infrastructureMulti-sig wallet and treasury management experienceExperience building multi-tenant SaaS productsFamiliarity with advanced frontend libraries such as:@xyflow/react@dnd-kitJotaiSWROpen source contributions or demonstrable side projectsWhy Join Worklo?Greenfield opportunity with major technical ownershipBuild cutting-edge infrastructure combining SaaS + blockchainInfluence architecture from database to smart contractsWork on products used by real agencies and consultanciesRemote-first, async team with strong engineering autonomyImmediate product impact with room to shape long-term systemsIf you’re excited about building scalable SaaS platforms while architecting real-world blockchain payroll systems, this is a rare chance to work at the intersection of enterprise software and decentralized finance.

This platform is a Decentralized Trading & Exchange platform designed to provide a transparent, trustless, and fully on-chain trading platform.With the core being an on-chain orderbook matching engine, Platform helps traders to have full control over their orders while reducing transaction costs and remains the same trading experience in a Centralized Exchange.V1 is built for EVM blockchains and is completely permissionless. Partners can work with Position Exchange’s on-chain central orderbook to share liquidity and power unique features for a better user experience.V2 will support follow things:- SwapIn the Swap of DEX Interface, the EVM tokens (ERC-20, BEP-20) are supported.- BridgeDEX Bridge is software protocols that **facilitate the movement of assets and data between different blockchain networks**, enabling interoperability within the decentralized finance ecosystem. EVM tokens (Ethereum, BSC, Polygon, Arbitrum, Optimism), Internet Computer and Bitcoin are available.So we are currently seeking talented Senior Software engineers to expand our development team.