This list deliberately leaves “tiny version of Redis, Kafka or SQLite” territory behind. That was the first list of 20 primitives. The more interesting search space is a primitive that introduces a new operation, one developers might eventually feel should have existed all along. Some research paper or niche project has probably explored pieces of these. They’re meant as category-level concepts, not smaller copies of familiar products.

Forty primitives

1. Reach. Store a current state plus transition rules and continuously maintain which states are reachable from here: REACHABLE(current_state). A database answers what is; Reach answers what can happen. Uses: AI agent safety, workflows, infrastructure, manufacturing, cybersecurity attack paths.

Run the 20 primitive project ideas through the four-question screen strictly and the ranking changes a lot. Several technically attractive ideas turn into weak projects. The economic buyer is unclear, free infrastructure already solves the problem well enough, or the moat amounts to “ours is smaller.”

So Statefile, Lease, BareQueue, TTL, Count, Remember, Freeze and probably ConfigLog go out at this stage. They all solve real engineering problems, but the money question is poor. Redis, SQLite, existing Go libraries, message queues, object storage, Git and cloud infrastructure already give acceptable answers. A tiny implementation might make a respectable GitHub project. “Simpler and smaller” doesn’t tell you who eventually writes a meaningful check.

App ideas cost nothing. Every one of them looks shippable in a weekend, and then the weekend turns into three months of auth flows, sync bugs, review notes and a paywall that took longer than the app.

So before Xcode or Android Studio opens, put the idea through four questions and write the answers down. Who pays? What problem does it solve? Can you say what it does in one sentence? Why would anyone switch, and what stops Apple from copying it? Ask them in that order. Money goes first because it kills weak ideas fastest, while a kill still costs an evening.

Every app idea has a boring 90% and a nasty 10%. The boring part is CRUD, auth, a settings page, Stripe. The nasty part is the one subsystem that decides whether the thing works at all, and it’s usually not the part that looks hard in the pitch. Below are nine builds worth attempting, with the nasty 10% named up front so you can decide whether you want to spend your weekends there.