For figuring everything electrical nothing else even comes close. Try the free trial of Electrist and see why electronic engineers in some of the finest R&D laboratories in the world, industrial maintenance crews, power utilities, RF & audio engineers, circuit designers, telecom engineers, and Ham operators have rated it the top electrical and electronic engineering tool for Palm OS. With the most advanced user interface and features available, and formulas found in no other software backed up with world-class customer service, it's no wonder!
Electrist does NEC ampacity look-ups to quickly get wire and cable sizes for any application in both the AWG and Metric standards. You can also enter any conductor properties and accurately find the voltage drop.
Size 3 phase panels & transformers with the built in load calculator. Enter any number & configuration of delta or wye/star and 3 phase, line-to-line, line-to-neutral, and/or centertap-to-neutral to instantly get both the phase and line loading in current, true power, and apparent power. Hundreds of formulas & variations:

Ohm's Law/Watt's Law
Resistor Color Code
Series/Parallel Resistance/Inductance/Capacitance
Unknown Value of Parallel Resistance/Parallel Inductance/Series Capacitance
Voltage/Current Dividers
Capacitive/Inductive Reactance
Series/Parallel Resistive/Inductive/Capacitive Impedance - in parallel, series, and as current
Peak/Peak-to-Peak/RMS/Average Sine Wave Conversion
Wavelength/Frequency/Period/Velocity
Delta/Wye Conversion
RC/RL Time Constant
dB, dBu,dBm,dBW,dBuV,dBV (with either equal or unequal impedances)
VSWR
Resonant Frequency
Periodic Waves
Conductor Voltage Drop (single or parallel conductors)
Conductor Size Selection (single or parallel conductors)
3 Phase Load Balance
3 Phase Voltage Unbalance - both NEMA and IEC negative sequence
3 Phase Active, Apparent, & Reactive Power
Cost of Use