It's called RotoMan (Rotoscope Manager), and it allows you to easily keyframe objects to follow another object, making it appear that they're attached, without the need to create parent/child heiarchies or constraints.
Although I wrote it to help me with complex technical animation, I believe it can be usefull for character animators as well (for instance, making a ball track with a glove after a baseball player catches the ball).
This is the link for the download and the instructions. Suggestions, comments, and bug reports are all welcome through this thread (so that everyone can see the comments and reply). Thanks for your help!