cosmic.voyage is a tilde community based around a collaborative science-fiction universe. Users write stories as the people aboard ships, colonies, and outposts, using the only remaining free, interconnected network that unites the dispersed peoples of the stars. If you would like to join us, contact tomasino [at] cosmic [dot] voyage.
A grassroots peer-based education project based around online learning and remote collaboration between small groups of students. They just started up so things are a little thin at the moment. This is an interesting experiment to keep your eye on. Creative Commons.
A collaborative textbook written by teachers opposed to the Texas School Board's revisionist view of American history.
volunteer effort to improve the state of Open Streetmap in places that are generally ignored by other maps because they're too far away, too rural, or otherwise unprivileged or underserved. NGOs and first responders rely on OSM during disasters. They can also rally mappers to develop datasets in specific locations at need (after disasters, usually).
A portal site at which people share calendars of various sorts which you can watch using Outlook, Thunderbird, Sunbird, or Google Calendar. In Apple iCal format (which is fast becoming a standard).
A mailing list for which you can sign up and potentially be tapped as an expert source by a reporter writing an article. You're not obligated to respond but you can if you so choose and have the time.
Gitlab is a F/OSS clone of everything Github's website gives you, from collaboration apps to bug tracking to an easier way to use Git on the server side. The repositories here are either their own software, or their own forks of software that Github makes use of. Requires Ruby on Rails.
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