CoFoundersLab - Meet 250,000+ entrepreneurs online
Founders Nation - Find or become a startup cofounder
Startup Stash - A curated directory of 400 resources & tools for startups
Supersourcing - Supersourcing is a platform that allows you to hire a professional freelancer in many fields.
Co-founder Question Cards - Questions to ask your co-founder to know each other better.
StartupResources.io - Tightly curated lists of the best startup tools