Bit on the weirder submissions for YC but our family genome sequencing facility is generating more than $500/mo on the side.
Currently growing at over 100% YOY (somewhere around 26% QOQ), closed out our last month at over $23k, and on pace to do somewhere between $350-400k. This is not an easy side project and there's been an insane amount of learnings on both the wet lab and informatics side. We've had some set backs but it's worth it when we get to hear what sort of life changing (literally) work we get to contribute.