Some business-y ideas:

1) Build an affiliate site. Some of the older posts on /r/juststart [0] are helpful.

2) Organize information and sell it. See the stuff made by Pieter Levels [1] or BuiltWith [2]. I just put together LotsofOpps [3] (which is just bunch of information on online/offline ways to make money). There is lots of info out there that will be interesting to someone if you can find the right angle.

3) Unbundle Craigslist [4]. Craigslist is terrible for some things. I'm working on BuiltRigs [5].

4) Unbundle Zapier [6]. A great example is BannerBear [7].

None of these things are particularly easy. Marketing is the hard part, but it's most important to actually build something and release it quickly.

[0] https://old.reddit.com/r/juststart/

[1] https://twitter.com/levelsio

[2] https://builtwith.com/

[3] https://www.lotsofopps.com/

[4] https://thegongshow.tumblr.com/post/345941486/the-spawn-of-c...

[5] https://www.builtrigs.com/

[6] https://kamerontanseli.ghost.io/first-it-was-craiglist-next-...

[7] https://bannerbear.com/