I guess everybody has those. I certainly have them, lots and lots of small projects where I tried out some new technology/language/framework, or implemented some small idea with it, ordid some exploration on a dataset etc. They all live with dubious names in a folder in ~/dev and over time, I just forget about them. Sometimes I accidentally find them again when doing something related (same task, different tool, or so), sometimes not.
Do you somehow keep track in a more elaborate way? Spreadsheet/database/notes?
It’s not perfect, but it works for me.