Software for Experimental Rocketry
Most of the software I use is from other sources.  Richard Nakka prime among them.

But I have developed a few bits and pieces that work OK and serve their purposes pretty well.  

KnCalc:  A little VB utility I wrote while taking a programming class.  Not real user-friendly at first, but great for getting quick calcs of prospective motors.  I still use it a fair amount.  
Click Here to download software (.zip file)
Click Here for instructions on installing and using it.  

BATESCalc:  Excel* spreadsheet to calculate the progression of Kn ratios for BATES grains of ideal and not-ideal length.  

UninhibCalc:  Variation of BATEScalc for uninhibited grains.  

Coneburner:  Calculates Kn ratios for motors using a deep cone configuration.  
Endburner:  Calculates Kn ratios for end-burning motors.  

Being spreadsheets, these can be easily modified, or incorporated into more sophisticated spreadsheets.  

* Don't have Excel?  These also run under Open Office Calc, part of a FREE office suite from Sun Microsystems.