Blender used to get a lot of stick about it's UI, but it's now it's doing amazingly well. It seams to be freeing 3D from Autodesk.
GIMP seams to be going through a bit of a development phase and after GTK3 move is complete, other features will get the that development. It could be interesting few years.
As for trying RISC OS, no where is especially active to be honest. Though it can be run on Raspberry Pi. The big thing it still does best is save dialogs. Just drag into a file manager window. For the decades after leaving RISC OS I have to copy paste directory paths like a primitive! The ROX Linux desktop gives you a bit of a taste of it, but only ROX apps have the dialog magic. Last I run RISC OS was ArcEmu to play Bug Hunter 1 & 2. I did some open source work on RPCEmu to run games I made as a kid. I should run it again to show the kids what I was doing at their age!
Problem is it is used to clean out copyleft too. Copyleft is a social good version of copyright. Using AI to wash it away, along with authorship, is not ok. Lots of open source wouldn't have taken over if it wasn't for stickiness of copyleft breaking "the tragedy of the commons".