The Gnome runner and Krunner from KDE both do this. I'm not sure if the Gnome variant supports arbitrary commands like Krunner does, but they at least have opening applications, unit conversion, and web search.

It's not the same.

He means something that can access all commands available in a given application, not a launcher.

Ubuntu's Unity has that, giving search access to all the menu entries in the opened application.

Sublime Text implementation is even more powerful, giving search access to all commands, and the list includes commands provided by extra packages added to Sublime.

So I can do, for example: 'ctrl+shift+p', install package, gitsavvy, <enter>; 'ctrl+shift+p', git diff current file, <enter>;