What I like most about IdeasNest is how low the barrier is. You don't need a pitch deck or a polished plan, you just answer four simple questions: who it's for, why there's demand, who your ideal customers are and how you'd reach them. That structure forces you to think clearly, and it gives people reading your idea something concrete to react to, so the feedback is useful and not just "cool idea, good luck".
It's also free with no paywall, and nothing pushes you to give away your IP, which removes the usual fear of sharing early. The private nests are a smart touch too. I work with cohorts and training groups, and having a closed space where a group can share ideas only among themselves is exactly what those settings need.
Full disclosure: I know the maker, and I've seen how much care went into this. Happy to see it live.