SmartCalc

SmartCalc is software for solving questionable science problems, its intention is to offer you what other programs can't offer. SmartCalc is checked by engineers from various sciences .
SmartCalc is freemium that means the program is free but there are some features that you can buy, in SmartCalc's case it is 'Custom mode' for building your own formulas.

This build of SmartCalc includes only GUI version.
Keep in mind that SmartCalc is in development.