> I've also noticed that a lot of successful solo projects seem to be network/directory platforms - i.e. building an audience through free content that you then monetize through commercial partnerships.
Startup directories like ProductHunt, BetaList, AngelList are all great examples.
Now that I think about it, that actually describes a lot of blogs/vlogs/podcasts too (create an audience with great content, monetize via advertising). Not quite SaaS, though, so slightly different from OPs original question.
Places like https://designacademy.io/ sit in the middle - content-first to create the audience, then use that audience to sell online courses in your given niche.
The takeaway - which applies to any business really - is that you need an audience and you need to be selling something that someone desperately needs (rather than something that someone "wants").
Recruiters need candidates. Advertisers need eyeballs. Companies need investor networks. Find the need, build the audience.
Nailed it! What others have you noticed?