Tower Unite supported libretro in February of this year. I think it should be listed on the Powered by Libretro page. But until now, it seems that no one had take note of it.
For details refer to: https://forums.pixeltailgames.com/t/emulation-with-libretro-tower-unite/46512
Tower Unite is an online playground sandbox that is independent from gmod and supports VR. I personally think it is similar to EmuVR and New Retro Arcade, but it is online and even larger.