Founders Nation - Find or become a startup cofounder
CoFoundersLab - Meet 250,000+ entrepreneurs online
Startup Stash - A curated directory of 400 resources & tools for startups
Co-founder Question Cards - Questions to ask your co-founder to know each other better.
Supersourcing - Supersourcing is a platform that allows you to hire a professional freelancer in many fields.
Y Combinator Co-founder Matching - YC’s free online platform to help you find your co-founder