Gatherapp.gg
Weekly availability for esports teams and groups. Everyone marks the hours they can play, the week shows the overlap, and one link posts it to Discord.
Finding an evening that works means a poll, twenty replies, and someone still missing. The answer ends up in a Discord thread that has scrolled away by Tuesday.
Everyone taps the blocks they can play. The plan view counts the overlap across the week and points at the blocks the whole team can make. Scrims and matches get booked on a block, and the week shares to Discord as an image, so nobody has to open the app to read it.
Most of the work was in the database, not the interface. Who can see and change what is decided by row level security, and a test suite tries to reach another team's data from the wrong account before anything ships.