Linkages, 4-bar mechanism, and other multi-bar mechanisms are useful for many robotic applications such as robotic grippers, payload bays, arms, legs and a variety of other robotic limbs.
The WATT Mechanism Suite from Heron Technologies provides a software solution for designing mechanisms from arbitrary motion paths.
The user interface was easy to use and I was able to produce a simple four-bar mechanism design in under an hour. WATT outputs a variety of information such as the path error and velocity in excel format and can export geometry information in DXF. While, it was not initially obvious to me when the software encountered a problem due to the mechanism jamming, the software generally produces good results for a wide variety of cases.
The list price for a single-user copy is 1575.00 Euros, however there is a 50% educational discount available for qualified organizations.
If you are on a budget you may want to consider The Geometer's Sketchpad which is available for $39.95. The Geometer's Sketchpad is a software program designed for use with "smart" whiteboards. The animation mode can be cleverly used to cheaply produce motion simulations for multi-bar mechanisms without having to resort to pieces of cardboard and Brass Fasteners.
The linkage library provides some good examples of what the software can do if you are persistent enough to figure out the interface. It is helpful when learning how to use the software to remember that "smart" whiteboards are lucky to have one mouse button, and that a line can be defined by two points. Once you manage to figure out the horrible user interface, The Geometer's Sketchpad turns out to be a pretty good program for the price.