Recently, I wished to use a trivially-simple TODO-list application whilst working on a project. I had a look through what was available to me in the "GNOME Software" application and was surprised to find nothing suitable. In particular I just wanted to capture a list of actions that I could tick off; I didn't want anything more sophisticated than that (and indeed, more sophistication would mean a learning curve I couldn't afford at the time). I then remembered that I'd written one myself, twelve years ago. So I found the old code, dusted it off, made some small adjustments so it would work on modern systems and published it.
At the time that I wrote it, I found (at least) one other similar piece of
software called "Tasks" which used Evolution's TODO-list as the back-end data
store. I can no longer find any trace of this software, and the old web host
projects.o-hand.com) has disappeared.