I used FreeCAD to create my objects. It has quite a steep learning curve but it works for me.

I heard good things about TinkerCAD which should be easier to use for some quick ideas.

A 3D-Printer, I thought I just play around with it and get bored, but you discover so many things that you can do!

The handle on the fridge broke? Print new ones. Need a Flowerpot? Just print one. The router needs a wallmount? I have one ready in a few Hours.

Also I can watch it print for hours, very fascinating and calming.