First tranche of 50 open invites to C̶a̶r̶t̶m̶a̶n̶l̶a̶n̶d̶ the refactorcamp mastodon instance. This link will be good for 50 signups/6 hours (~4PM Pacific today)
https://refactorcamp.org/invite/dxCUa4zn
Mastodon is basically open-source federated twitter.