Stock research platform using relatively cheap ($X00/yr)fundamental data & free pricing APIs.
Had a fun "fight" with a major pricing website for a game. When your (rate-limited! trying to be nice!) crawler needs to turn to OCR to defeat css spriting and they're leaving comments in the HTML though... a bit too combative. Fun project making it work though.
Any game with an economy I end up making stuff for. Personally, I wish games weren't so hostile to automation or user time these days!
I also once SaaS'd a weird file format translator thing on heroku for myself; sometimes old formats or algs do really just disappear!
I've made some small modules for my MagicMirror but haven't had inspiration on further stuff for that just yet.