In case it's relevant, host and guest are both on macOS.

Things I want:

1. multi cursor (each user can edit simultaneously)

2. each user has their own keybindings, theme, etc so that the guest doesn't have to guess the host's keybindings

3. super-fast

4. decentralized for security purposes. In other words, nothing is sent to another party or server

5. prefer something free

6. not require creating an additional user in the OS (thinking of tmux here, to do things safely you should create a restricted user that your guest ssh into)

I'm aware of:

* [TypeInTandem](https://github.com/typeintandem/nvim). Might work? Haven't dug into it yet, though their website http://typeintandem.com/ can't be found and there's no commits in 2 years.

* [CoVim](https://github.com/FredKSchott/CoVim). Not actively developed and I'm not sure it even works anymore?

* tmux. Doesn't allow 1, 2, or 6 above, plus conflicts with vim keybindings which is annoying.

* [floobits](https://floobits.com). not free (#5 above) and not decentralized (#4 above)