Oracle, for one, has had it for a long time.

"Use the COMMENT statement to add a comment about a table, view, materialized view, or column into the data dictionary."

https://docs.oracle.com/cd/B19306_01/server.102/b14200/state...

Also PostgreSQL (since 7.0, released in 2000):

https://www.postgresql.org/docs/current/static/sql-comment.h...

Also mssql, the extended property ms_description can be applied to objects and columns and appears in SSMS as comments.

> It's not meant to be user-editable

I think that's kind of a stretch since regedit has been a part of windows as long as I can remember.

I'd say regedit is not really the preferred method for anyone to interact with the registry though.

I'd say that regedit is integral to day-to-day use of Windows.

Well I don't know what in the world you're doing but I almost never use it.

> arcane troubleshooting stuff

... is exactly the reason to have useful comments in there.

Config files do, which is what the Registry replaces.