Distributed systems, databases, and concurrency at the level they actually break.
The foundations every senior engineer is expected to have and very few actually do. Consensus, replication, storage engines, concurrency primitives, and the reasoning tools behind them. Every challenge ships with runnable code in Go / Python / Rust / Node and three labelled prompts so your AI can teach the mechanism, not paper over it.
100 challenges to take you from `python --version` to shipping a FastAPI + Celery service with full observability — and the canonical 2026 RAG pipeline as the capstone.
100 challenges to take you from `node --version` to shipping a multi-tenant Fastify + BullMQ + Prisma service with pino, OTel, and a Docker image you'd put on production.
100 challenges to take you from `go version` to shipping a production Go service with OTel, structured logs, graceful shutdown, and a Docker image small enough to fit in a tweet.
100 challenges to take you from `cargo new` to shipping an async Rust service with axum, sqlx, tracing, and a webhook delivery worker that fights real network failures.
Deep internals, concurrent features, React Server Components, advanced patterns, and production-grade state management — everything you need to build React applications that are fast, correct, and maintainable at scale.
Build React applications that feel instant by updating the UI before the server responds — with correct rollback, conflict resolution, and offline support.
100 challenges — from your first MongoDB insert to reading WAL files, tuning autovacuum, and orchestrating a zero-downtime schema migration on a 100M-row table.
Ship a real money-moving product — payments, ledgers, compliance, payouts, BaaS, custodianship. Engineering, regulatory, and ops literacy fused.
100 challenges — from reading a curl waterfall to finding the index that makes your p99 drop from 4s to 40ms.
100 challenges from CQRS and CDC through Kafka, distributed transactions, time-series, object storage, streaming video, multi-region deployments, Lambda/Kappa architectures, and database internals deep cuts.
A server that works for 10 users breaks at 10,000. Rate limiting, caching, load balancing, queues — one module at a time.
100 challenges, from race conditions on your laptop to consensus across continents.
Three parties, one answer, zero inputs revealed. Build real MPC from shares and OTs up to threshold ECDSA wallets and sealed-bid auctions — 100 challenges in Python and Rust.
A practical, milestone-driven playbook: what breaks at each step (100 → 1k → 10k → 100k users) and what to add — not in primitives, in moves.