Airesis
eDemocracy
Bluedoc
document management tool
brief-ideas
journal for brief ideas
Canvas LMS
enterprise-grade learning management system
Coursemology
open-source gameified learning platform
Danbooru
taggable image board
Discourse
next-generation discussion platform
Fairmondo
free market place in the hand of the users
Feedbin
open-source feed reader for multiple platforms
FeedBunch
simple and elegant reader
GitLab
self hosted Git management
Listed.to
online publications with automatic newsletters
Mastodon
distributed, interconnected microblogging
OneBody
church management software
OpenProject
project management system
openSNP
annotate your SNP-set
openstreetmap.org
crowd-sourced map of the world
Organization for Transformative Works Archive
archives of fanworks, including fanfic, fanart, and fan vids
pinballmap.com
source code to pinballmap.com
planningalerts.org.au
planning alerts for Australians
PublicLab.org
collaborative knowledge-exchange platform
rubytoolbox.com
catalog of all Rubygems that keeps track of popularity and health metrics
TagTeam
social tagging for academics
Tracks
software for implementing David Allen's Getting Things Done™ methodology