Comment by rogual

* A preprocessor that writes C++ header files for you, so you can write things more like you would in Java or Rust, i.e. just once. I use this for most of my C++ code now, and sometimes I forget it's not how C++ really is.

* A board game server for playing Scrabble over the internet, without either having to change it enough to not get sued, or withstand whatever crap the licensed apps do. Can't be released for obvious reasons.

* A server that runs on a Raspberry Pi connected to my digital piano via MIDI, recording a MIDI file of everything that ever gets played. No more "drat, I wasn't recording".