Founders Nation might be a bit more popular than Y Combinator Co-founder Matching. We know about 1 link to it since March 2021 and only 1 link to Y Combinator Co-founder Matching. 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.
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: almost 4 years ago
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 3 years ago
CoFoundersLab - Meet 250,000+ entrepreneurs online
Findnlink - Find people to work with on your ideas.
Founder's Prenup - Dating Co-Founders? Secure what's yours!
Co-founder Question Cards - Questions to ask your co-founder to know each other better.
Co-Founder App - Find your perfect co-founder
Team of Teams - http://teamofteams.io/ digital platform helps young co-founders to match by their professional core values with help of ML.