FSearch [Fast searcher of all files on my computer. Like Search Everything for Windows but worse in many ways]
AudioBookshelf [Podcast server]
I use all of those pretty regularly. Honorable mention on iOS is a program called Is It Snappy? which helps me measure input lag. It doesn't collect any data or run ads (rare trait on a phone app). I actually made a purchasing decision with the help of this thing to correctly conclude that the Nintendo Switch Pro Controller had a noticeable input delay (enough to make me return it). The funny thing about that was if I just looked up spreadsheets others have done I would have seen that same conclusion there, too, without having to go through the effort of buying it myself :P.
PikaBackup is more of a Time Machine style backup system. Not just for Gnome, it simply is made with the GTK.
Ultimately, I went with a Sony DualSense for my latest gaming controller. It has low latency when wired and the buttons are not clacky. Solid construction. I also have an 8BitDo Pro 2, which has one thing I especially like -- hardware turbo buttons. The rest of the controller is merely OK, and IMO not worth the extremely high praise it otherwise receives. Serviceable controller.