I am one of the developers of OpenToonz and I have recently added some new Stop Motion features to the program.  For now they are in a OpenToonz based program called TurtleMotion.  There is webcam and Canon DSLR support.
It is Windows only for now, but Mac should be possible sometime soon.

It is still in early development stages but is ready enough that I'd love to share it with you.  You can try out alpha builds here:
https://github.com/turtletooth/OpenToon … ag/0.0.0.3

Please let me know what you think.