Undoubtedly the "Bob" family of tools for how much they expand the functionality of TW. They have changed how I use TW.
BTC's work. Muuri ("touch" version); KeeBoord. Also the early stage Midi music player with a notation system (
http://musicsheets.tiddlyspot.com/). I like his stuff because it deals with some really useful things that haven't been done before--and you can kind of watch him develop them over time which is itself instructive.
I'm leaving out many because their first releases go back to 2017 or before.
One general point: this year has been phenomenal in finesseing, the now many, ways of saving.
J.