Probably not exactly what OP means by "side project" but in 2006 I started working towards getting FreeBSD running on EC2, and I got it working in 2011; I've been the maintainer of the FreeBSD/EC2 platform ever since.
This started because I wanted to use FreeBSD in EC2 for Tarsnap, but I'm now getting sponsorship from Amazon for my work on FreeBSD (EC2 and release engineering) as well as a much smaller amount from a Patreon I set up a few years ago.
This started because I wanted to use FreeBSD in EC2 for Tarsnap, but I'm now getting sponsorship from Amazon for my work on FreeBSD (EC2 and release engineering) as well as a much smaller amount from a Patreon I set up a few years ago.