Using it with a touchpad is far from ideal, but you should be able to manage it by drawing the chain very widely around the gears. The chain will be tightened automatically.
Currently there's no todo list with features like other types of gears, more easily creating gears of specific sizes and the like, but I would very much welcome contributions of that type. I ported this version from the original in java, to make it usable on mobile devices, because they are much more widely available than e.g. wacom tablets.
I'm using the GearSketch environment in my PhD research to study different forms of support for learning about gears. For instance, I created a puzzle generator that creates concrete gear configurations based on abstract descriptions (e.g. there are two unmovable gears, one larger than the other; goal: connect them in such a way that the large gear will turn faster than the small gear). Using each student's solutions to earlier puzzles, the software tried to model their individual understanding of the gears domain and create new puzzles based on that. Turns out accurately modeling student knowledge is hard. ;)
The students using GearSketch are 10-11 years old, and understanding the interactions between the normal gears and chains is already quite challenging for this group, so my current focus is not on adding more elements. But like I said: I'd love to see others working on it and would be available to help.