Filter Wiz PRO [$69 US]
Advanced active filter designer with over 20 Approximations, 79 circuit topologies, built-in analog simulator and many helpful design aids. eSketch compatible.

Filter Wiz Lite [FREE]
Easy to use active filter designer with 5 Approximations (including Elliptic) and 32 circuit topologies. Far superior to freeware/online calculators. eSketch compatible.

555 Timer PRO EX [$29 US]
Best 555 timer reference available. All the features of 555 Timer PRO plus wizards for active filter design, photodiode amplifiers, op amp amplifiers and transistor amplifiers.

555 Timer PRO [$19 US]
Provides an array of design wizards, circuit blocks and information panels that facilitate the use of the 555 timer in electronic projects.

eSketch [$29 US]
A powerful schematic capture and simulation application specifically designed for the ultra fast rendition and simulation of frequency-shaping analog circuits.

Resistor Color Coder [Free]
Very useful for determining the color codes or values of 4 and 5 band resistors. Now includes Surface Mount Device (SMD) Markings Evaluator and E-Series Resistances.

BitRule [Free]
Much easier to use than other screen rulers and screen calipers. Obtain horizontal, vertical and diagonal distances, as well as the angle to the horizontal.

555 Timer free [Free]
555 Timer calculator with 4 modes -3 astable and 1 monostable.
Can set frequency and duty cycle (or pulse width).
Can scale capacitors