Files sync, contact, calendar, password managers...
Websites, blog, wiki, CMS...
Chat, email, forum, meetings...
Collaborative text editing, spreadsheets...
Tasks, polls, accounting, ERP...
Pastebins, URL shortener, proxies...
Newsfeed readers, books library...
Music library, pictures gallery, P2P, TV shows...
Microblogging, federated media
Wanna have some fun? ;)
Git forges, apps skeleton, CI, translation...
Monitoring, backup, network, DB tools...
Home automation, energy dashboard...
Weird experimental or very-custom stuff