I have a few. partkart.com (now defunct) - it was supposed to be thingiverse but for cnc projects. I made it one summer when I was in school and had the naive

I have a few. partkart.com (now defunct) - it was supposed to be thingiverse but for cnc projects. I made it one summer when I was in school and had the naive notion that users would find it organically or through cnczone. I think one or two people used it total after a year. Learnings: have a plan for user acquisition. partkam/makercam - browser based cam system, made during that same summer. Some people actually used this, as it solved a legitimate problem. I wasted a lot of time developing a custom polygon offset algo, and it was written in flash/actionscript cause it just had to be a web app. Learnings: don't develop for dying platforms, use libraries. deepnest.io - nesting app for laser cutters. There are similar commercial apps so the market exists, just not sure how to reach the SMBs that are presumably the end users. Learnings: don't make an app that requires high touch sales if you have no idea how the industry works. final learning: I actually enjoyed working on this stuff and learned a ton, even though they weren't ultimately successful. Having them contributed to getting a job after I graduated and later, more successful projects.