The PICO-8 community uses Slack for real-time discussion and collaboration. The "pico-8" Slack group has active users and multiple channels.
To join this Slack group, sign up for Slack, then enter your email address in this form:
https://slofile.com/slack/pico-8
You will be invited to the Slack group automatically.
Discussion: http://www.lexaloffle.com/bbs/?tid=2732
There is also another Slack group called "picocity": https://slofile.com/slack/picocity http://www.lexaloffle.com/bbs/?tid=3157
The Fantasy Consoles Discord server has a PICO-8 channel, as well as channels for other fantasy consoles inspired by PICO-8 and otherwise. The community runs regular game jams: http://discord.gg/sFeDxWK