Writing software for GNOME.
https://en.wikipedia.org/wiki/Vala_(programming_language)
https://en.wikipedia.org/wiki/GObject
KDE is based on Qt GUI library, and Qt is C++.
GNOME is based on GTK GUI library, and they wrote their own object system (GObject) on top of C. Then they wrote Vala, which updates plain C to be more like C# or Java, so it's easier to work with GObject than by using plain C.
I also liked the itemwise comparison with Java: https://wiki.gnome.org/Projects/Vala/ValaForJavaProgrammers
Defining a new language "just" for the GTK library will likely be responsible for it not taking off that much, even if - as is the case here - the language looks neat. The fact that it compiles to C, which is universally available, and the fact that it is not associated with corporate interests (unlike Microsoft C#/.net and Oracle Java/JVM) could be interesting, but perhaps decoupling things from GTK could have been wiser to get more reach?
I mostly develop software libraries nowadays, and the only GUIs are Webguis to interact with REST services, but for those folks that make the Linux desktop a better place, this seems a good way to be more productive than in C.
Speaking of which, the Linux desktop needs a re-think: someone should start and re-develop all apps in a much more clean and homogeneous way so that it is obvious what is done how. The existing bag of tools from different decades, inclusive apps from xfig, xlock, xv over LibreOffice/KWrite to gedit/kedit are just an inconsistent mess; even MS-DOS apps managed (at some point) to stick to standard text menus, from EDIT to TurboPascal.
https://www.theregister.com/2024/01/24/rise_and_fall_of_cua/
I have no doubt that the Java world has excellent tech behind the AOT support but the footprint is simply not comparable when you can't even construct a java.lang.String without bringing in the entire JapaneseChronology.
That said, it only really shines for the "gtk based linux desktop" usecase, for everything else the situation flips around, as you now need to bring your own GTK. Occasionally still worth it embedded, but not much else.
But the GNU/Linux camp was rather hesitant to adopt .Net for fear of Microsoft suing people over patent issues. At least that is my memory of it. People wrote replacements for those apps Tomboy -> gNote, F-Spot -> Shotwell, Banshee -> ???, using Vala.
Now that Microsoft has made .Net open source, the lawsuit threat seems to be gone (at least for the foreseeable future), but I think the ship has sailed.
Pretty much everyone reverted back to Rhythmbox, which to this day still feels less polished somehow.
There is also now an option to statically link native libraries into NativeAOT binaries in .NET, and to statically link NAOT-compiled .NET libraries into existing C/C++/Rust binaries.