Huntathon - Browse and submit Product Hunt Global Hackathon projects
QuizUp - QuizUp gives you the opportunity to test your trivia skills against friends and strangers throughout the world.
Foundler - Online hackathon weekends. Attend every other week.
2016 Photo Challenge - Take a photo every day for 366 days
Confs.tech - Open source list of tech conferences: JS / Ruby / Data etc.
Woolah - Knockout Photo challenges with your friends.