I have some applications that aren’t in any repository but simply came as portable .zip files. How can I add those to the GNOME shell?
(I am not sure if I use the right GNOME terminology here. I mean where all the installed apps are listed. :))
I tried to add a .desktop file in .local/share/applications but nothing showed up. Any hints would be very welcome. 
And write it yourself? If it is not valid, it will never show up.
desktop-file-validate ~/.local/share/applications/app.desktop
Thanks! Now they show up. They even validate but nevertheless they don’t do anything. The apps don’t start. I will have to experiment with the options a little.
To get it working I had to change all paths in the .sh file the .desktop file is supposed to start to absolute paths.
For example:
#!/bin/sh
#export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:./lib/
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/myuser/games/rigs-of-rods/lib/
#./RoR "$@"
/home/myuser/games/rigs-of-rods/RoR "$@"
What’s the reason for that? Is this normal?
I save myself from headaches. I installed Desktop File Creator and gave it a little custom icon, made the .sh executable in the terminal chmod +x script.sh
and that’s it. Enjoy life.