Plotinus is a library that adds a searchable command palette to any GTK+ 3 application, similar to the Atom and Sublime Text Command Palette feature (or Unity HUD).

You're probably familiar with the Unity HUD, or Head-Up Display, which lets you search through and application's menu. Thanks to Rafael Bocquet's i3-hud-menu (and J.A. McNaughton's fork), you can use this menu search feature in pretty much any desktop environment (and in any Linux distribution in which you can install unity-gtk-module).

i3-hud-menu allows searching and navigating through an application's menu using the keyboard, with the use of dmenu (dmenu doesn't have mouse support by default). Here's how it looks like in Xubuntu 16.04:

By default, the popular Eclipse IDE does not support the Ubuntu AppMenu or  HUD. The reason for this is that Eclipse has been blacklisted so it wouldn't use the AppMenu around the time of Ubuntu 10.10 Maverick Meerkat because it didn't work back then.

Now Eclipse does work with the AppMenu, however, there are some minor glitches like some menu shortcuts not being displayed (although they do work). If this isn't a problem for you, here's a quick way to whitelist Eclipse so it can make use of Ubuntu's Appmenu and HUD.

HUD was added by default in Ubuntu 12.04, but only for Unity 3D (with Compiz) and since feature freeze has passed, it seemed HUD wasn't going to be available for Unity 2D. But a feature freeze exception was made and Unity 2D now includes HUD.

Back when Mark Shuttleworth announced HUD (Head-Up Display), a new smart menu for Unity, it wasn't sure if it will be added by default in Ubuntu 12.04 Precise Pangolin. Well, Unity 5.4.0 has just been uploaded to the Ubuntu 12.04 repositories and it comes with HUD by default. However, HUD doesn't replace the global menu so it you're not forced to use it!

A while back, Alex Fiestas has implemented something very similar to HUD, Unity's new smart menu, for KDE. The initial implementation only worked for KDE applications and only if the menu was shown in the application window. After seeing HUD in action, he was motivated to continue his project, so he implemented this into KRunner.