If you want to start simply tracking few things and you are on Android, I highly recommend https://loophabits.org/ https://loophabits.org/ (FOSS, F-Droid, Play

If you want to start simply tracking few things and you are on Android, I highly recommend https://loophabits.org/ https://loophabits.org/ (FOSS, F-Droid, Play Store). It is sleek and very usable.