[com2kid]

More in terms of UI.

Notepad++ has what you need to edit a file and not much else, but it also has a decent plugin system.

[have_faith]

ST almost has no UI when opening a single file (no sidebar etc), would be curious how it could be more minimal.

[nicoburns]

Check out the view menu. Pretty much all the UI bar the actual text you’re editing can be easily hidden.