Supposedly has a level editor and Workshop support, but there is no actual in-game editor, there is no workshop for levels to show up in, and it seems the devs abandoned the idea completely...

Claims to have a level editor (even has a screenshot on the store page of user created levels), but it doesn't seem to load no matter how long you wait...

While there's no Workshop, it's fairly easy to add in levels/campaigns as long as you know where to get them (scmapdb.com for instance) and where to install them.

Workshop compatability. Same with Gold Edition.

Workshop compatability. Same with Don't Starve Together.

While not as mod-friendly as it used to be (namely and semi-understandably on official servers), modding is still entirely possible to do on community servers (if they don't have sv_pure on).

While an admittedly buggy game, it has good mod support and plenty of fun mods to play with and break the game even more (sometimes to the point of total unplayability...)

You can make your own "levels" using any music you want (as long as it's in a compatable format). Good enough for me. Also has ship mods/Workshop compatability with DLC.

The entire game is a level editor. It also manages to be robust and easy to use while not being completely overwhelming. Whether or not Worlds Adrift itself is good, this is a fun tool.

Probably one of the most famous (and infamous) moddable games of all time. Some argue you need mods to even make it a good game...