Are there any games, aside from Ps:Torment, set in the planescape multiverse on gog?

AFAIK, this is the only Planescape setting video game that was made. There is a spiritual successor title, Torment: Tides of Numenara:
https://www.gog.com/game/torment_tides_of_numenera

Haven't played it myself, but didn't a lot of people think that it didn't live up to the standard of Planescape:Torment?

Aye, I doubt that it could have lived up to those expectations. But, I have not played it myself, and I never finished Planescape: Torment either.

No it's just this game but there's Temple of Elemental Evil which is set in Greyhawk and dozens of other DnD games on GOG if you just want to try other DnD games and haven't played all of them yet.

Might not be Planescape specifically, but if you want games where you travel to other planes of existance:
* I believe Pools of Darkness has you travelling to other planes of existance.
* While not D&D, Bard's Tale 3 has you exploring other planes.
* While not D&D either, some of the Might and Magic games (2 and Xeen) have you exploring elemental planes, and 1 I believe lets you go to the Astral Plane.
* (Interestingly, apparently Daggerfall has an unused spell effect called Astral Travel; perhaps that spell would allow access to an astral plane if it were implemented? Then again, Daggerfall's world is big enough already.)