GNUBG already has nice panels with various race formulas, I think the Keith Count deserves a place there. It is both quite simple to learn and use and mostly more accurate than the Thorp and Kleinman counts. It doesn't give GWC directly but that may be solvable just as there is Bower's interpolation for the Thorp count.
Here's a link to the summary of the Keith Count, lots of other info are on the rest of the same page: