The half-dozen that I had researched that all came out around the same time:

  - https://calla.chat (my own, though I don't run it as a service, it's a component of my project at work)
  - https://mixaba.com
  - https://sococo.com
  - https://spatial.chat (which looks like a 2D version of Spatial.IO)
  - https://highfidelity.com (a 2D pivot for what was originally a VR project from one of the founders of Second Life)
  - https://hubs.mozilla.com

I'm missing one or two as I noticed that the main variation in total features could be covered with only a few of the ones I've listed and just stopped updating my notes doc).

Add in another half-dozen mentioned elsewhere in this thread (though I've not looked too deeply at most of them)

  - https://www.movement.fm/spaces
  - https://makespace.fun/
  - https://grouproom.io/
  - https://rambly.app/
  - https://www.huddlehq.io/
  - https://branch.gg/

These are just the ones that run in the browser. There are several more built specifically for VR (AltspaceVR, VR Chat, Spatial.IO, RecRoom, etc.), as well as some very long-running native desktop apps. 3D and spatial chat is a pretty long-running market.