One of the challenges of cigar box guitar building is determining how you are going to tune the guitar and what the chords are especially if it isn't a 6-string with standard tuning.
I discovered the Fret program (see link above) for Windows by Danny Chapman on the web and have found it very useful. You determine the number of strings and what notes they are tuned to. If you put in the notes backwards you can get Left-Handed chords which I find a real plus. It doesn't generate all the possible chords, but it will give you a pretty good start. You can display the chords on the screen and print them out.
One site that I have found helpful that has a variety of tunings and extensive chord charts for each is Brian's huge chordlist collection. Here is the link: http://chordlist.brian-amberg.de/en