A good friend emailed me to let me know that it's a "glorious day in the history of origami", because version 5 of an origami program called TreeMaker has been released (Mac, Windows, Linux, and its open source).
TreeMaker is a program for the design of origami bases. You draw a stick figure of the base on the screen; each stick in the stick figure (the "tree") will be represented by a flap on the base. You can also place various constraints on the flaps, forcing them to be corner, edge, or middle flaps, and/or setting up various symmetry relationships (forcing pairs of flaps to be symmetric about a line of symmetry of the paper, for example). Once you have defined the tree, TreeMaker computes the full crease pattern for a base which, when folded, will have a projection (roughly speaking, its "shadow") equivalent to that specified by the defining tree. The crease pattern can be printed out, or copied and pasted into another graphics program for further processing. Crease assignment (mountain or valley) are not computed, but with a few simple rules and some exploration by hand, the proper crease assignment can usually easily be found.