Y Combinator Co-founder Matching might be a bit more popular than Founders Nation. We know about 1 link to it since March 2021 and only 1 link to Founders Nation. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
You might get in contact with a nearby university, professor or student organization that have relevant courses to get in contact with students or alumnis. Other sources for co-founders are startup related meetups or websites (e.g., founders-nation.com). Source: over 2 years ago
One idea I just remembered is to find a business co-founder that already knows a market well and sees an opportunity. Startup School's co-founder matching service is quite good. Source: over 2 years ago
CoFoundersLab - Meet 250,000+ entrepreneurs online
Find A Maker - find a partner for your next project
CollabFinder - Find cofounders and makers to help build your project
Founder's Prenup - Dating Co-Founders? Secure what's yours!
Findnlink - Find people to work with on your ideas.
Co-founder Question Cards - Questions to ask your co-founder to know each other better.