Text editor, RSS reader, electronic schematic simulator, perfboard designer, optics simulator, browser, git GUI client, music player, expenses tracking app, spreadsheet app (I needed to make simple manual edit in many csv files and waiting for office just took too long, so I made just editor and it launches instantly), numerous one time use chrome extensions, calculator, libv8 based shell, video editor, ad blocker, ...

It usually reaches perfect usability for me very quickly, but to make it usable for others or make it publishable would take months.