I’ve been following the discussion on Emacs Devel about moving the excellent which-key app to Emacs core. Moving it to core was non-controversial. The only issue was whether they could get all the which-key contributors to assign their rights to the FSF before the Emacs 30 freeze. Happily, that appears to have happened and which-key will be part of Emacs version 30.
In a sense, it doesn’t really matter. As I’ve said before, the difference between core and third party packages is mostly political rather than practical. Still, there are some advantages to being in core. First, some users install Emacs on minimal systems or have to run old versions for one reason or another so they have to depend on whatever comes prepackaged with Emacs. Second, and more important to my mind, having a package in core aids in discoverability. It’s a lot easier to discover, say, which-key if it’s builtin and doesn’t have to be installed.
Regardless, if you aren’t already using which-key, you should start. It mostly stays out of the way but if you start a key sequence but don’t complete it within a preset time interval, which-key will pop up a menu in the minibuffer with the possible completions. It’s really great because you don’t have to worry about, say, all the rectangle commands. If you type Ctrl+x r and stop, which-key will tell you all the possible completions.
I’ve been using it for years and wouldn’t want to live without it. I’m happy to see it moved to core if only because a few more people will discover it.