Hmm, let's think about it for a moment. There isn't really that much I'd put into that category.
1. The MultiTab 6000. It saves so much time for some skills, it isn't even funny. It allows for multi-tasking, too.
2. The SwiftGro Gardening station. Helps enormously with the weeding and fertilizing. Speeds up growth with at least two pushes per day instead of one. The only negative aspect: it seems to be a bit of a performance hog, but that's a general thing with gardening.
3. The Head Start Playpen. I'm not necessarily using it for skilling, although it even does that, but for "storing" toddlers that learned everything they can from their parents directly. Works much better if you have two toddlers, because then you can forget your family has toddlers.
Honorable mention:
The Rim Rockin’ Basketball Hoop. Sims love it, plus they get their athletics a slightly different way.
