Three products we designed, built and still operate. Each case study covers the engineering decisions and what they cost, not the feature list.
A tracking page for repair shops — customers follow their repair on a live link instead of phoning to ask.
Notification delivery is idempotent under retries and reserves its quota inside the same transaction that creates it.
A free reference for the Islamic zakat threshold, computed daily from live metal prices across 11 languages and ~150 currencies.
Ships a real MCP server, an RFC 9727 API catalogue and llms.txt — machine consumers are a first-class audience, not an afterthought.
A portfolio tracker for Casablanca Stock Exchange investors, with weighted-average cost, capital-gains reporting and time travel.
Nothing derived is ever stored — positions, cash and P&L are recomputed from an append-only event log, and made fast by two cache counters.