Here are instructions on joining crabgrass on riseup.net
1. Create a personal account at https://we.riseup.net
2. One person from your coop can then create an organization
3. Invite your fellow worker-owners to your coop's organization
4. Feel free to play around with the crabgrass features and make notes on what works well and what is confusing.
The crabgrass URL is https://crabgrass.riseup.net