Y Combinator Co-founder Matching - YC’s free online platform to help you find your co-founder
Founders Nation - Find or become a startup cofounder
Find A Maker - find a partner for your next project
CoFoundersLab - Meet 250,000+ entrepreneurs online
Findnlink - Find people to work with on your ideas.
The On Deck Fellowship - An 8-week program for 100 of the best early-stage founders