Pull-up and pull-down resistors, water analogy
medium.com3 pointsby matiu1 comments
It is free and open source, using the MIT license
It uses human-readable text files for storage. It imports and exports JSON, so your data is never held captive
There is DOM access and a Hook script API
There are many available free and open extension scripts
There is Vit, a curses-based UI
There is FreeCinc, a free online sync service
There is Inthe.AM, a free online sync service, web UI and iOS client
There is Mirakel, and Android syncing client app
There is BugWarrior, so you can import your bug issues from a dozen different bug systems
It's just a model in my brain; it's probably wrong, so please be kind with corrections :)