Building some tools/machines
Some things you can buy, others you can't... or you can, but where's the fun in that?
My first project was a table router. The aim was a compact, portable router with a super stable fence and versatile fixing options. I nailed most of it on the first go, just had to redo the fence.
The stand-up belt sander is one of my favorite types of sanders. For my kind of work, it is absolutely crucial to have one.
My proudest creation is the metal bandsaw. It's so precise and easy to use. I don't even know why they don't manufacture and sell it as is in hardware shops.