We use Matrix/Riot chat in order to communicate. Our channel is open to the public, and also bridged with an IRC channel on Freenode.
We also have a separate Discord group chat set up.
- Chat in the Discord group at discordapp.com/invite/fATAd44
The older IRC channel is still used by some people, but does not have much active discussion.
- Chat at the 2600Net/#philly2600 channel