1. Ability to save a set of parts as a named template. You could then insert them into any level by accesing them from a pull down menu. It would work just like placing a rod or ball -- you get a ghost of the contraption and there's an X through it if it overlaps or doesn't fit in the blue box, etc. It gets tedious sometimes building the same set of wheels, etc, especially if you're using a touchpad on a laptop. This feature would allow me to quickly and easily piece together smaller premade parts into a bigger contraption. An example might be the base support for a catapult, or perfectly triangular vehicle. They would appear in a "my contraptions" area that I could also share with others.
2. This could be solved by just #1, but maybe a separate feature-- the ability for the contraption I build in the 'test' of a custom level to be persisted across multiple tests. If it happens that the last edit made it so the last contraption won't fit or isn't in the same location, then it can just delete it. If I move the placement area though it should follow it.
3. A checkbox that removes the 'welcome' screen on future visits.
4. While I'm moving a part, the keyboard arrows should move the part one 'notch' at a time, for easier fine-tuned adjustments.
5. While moving or resizing a part in edit mode, the new size/location should be relative to where in the handle box I clicked on. Currently if you have a really small part and you want to make it just a little bit different, you have to basically start over, because it 'jumps' over the size you wanted, since it depends on where in the handle box you clicked on to begin the operation, how far it thinks you moved.
6. Make the size of the game a little bigger. I suppose it is designed to work in small resolutions, but I have high resolution, and I always find myself zooming out immediately.
7. A 'grid' mode in edit mode that lets me snap parts to the grid.
8. The letters "goal" in the goal area dont always fit into the actual goal area size. If they dont fit I say just remove them. Example: http://fantasticcontraption.com/?designId=660986