I used to love
Capsella.
It was fun, easy to build stuff that moved. And despite my best intentions it actually taught me some basic mechanics; like how gears, drive shafts, and differentials work.
Speaking of obscure toys, does anybody remember a specific building block set? It was basically rings about 2 inches in diameter that had 4 legs. You could build all sorts of buildings with them. I'm just trying to remember the name of them.