NeoCal is available in several editions to match your needs:

Features Lite Scientific Financial Advanced
Multiple layouts
Dynamic keyboards
Optional RPN
User registers
Undo / Redo
Macro recording and playback
Fractions and Mixed Numbers
Functions Lite Scientific Financial Advanced
Percentages
Register arithmetic
Scientific Lite Scientific Financial Advanced
Trigonometric
Hyperbolic
Logarithic
Degrees / radians conversion
Time and angular conversions
Physical constants
Statistical Lite Scientific Financial Advanced
1 or 2 variable analysis
Weighted average
Linear regression
Probability
Financial Lite Scientific Financial Advanced
Time Value of Money
Amortization
Discounted Cash Flow Analysis
Internal Rate of Return
Net Present Value
Interest conversion
Margin and Markup
Date and Time Lite Scientific Financial Advanced
Date arithmetic
Duration arithmetic
Duration conversions
Programmer Lite Scientific Financial Advanced
Base number conversions
Integer math
Logical operations
Bit manipulation
Conversions Lite Scientific Financial Advanced
Length
Area
Volume
Speed
Weight
Temperature
Durations
Number base
Unit artithmetic