My partner and I are both software devs. She quit her job a year ago, and has been working on a few micro-businesses to try a) learn some new skills and b) diversify our sources of income. So far this year she has built:

* https://unofax.com - A simple a la carte fax service

* https://unopost.com.au - A way to send physical mail online (and avoid standing in line at the post office)

* https://snailgram.com.au - Custom greeting cards, with the message inside written by a 3D printer holding a pen.

There are a handful of others too, but these are the ones that are live so far. I've contributed between 5-40% to these projects.