Filter Wiz PRO [$49 US]
Advanced active filter designer with over 20 Approximations, 79 circuit topologies, built-in analog simulator and many helpful design aids. eSketch compatible.

Op Amp Selector [$12]
New searchable compendium of over 500 op amps indicated by manufacturers as being suitable for active filtering. Finding the right operational amplifiers is now easier and faster.

555 Timer PRO EX [$21 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.

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.

eSketch [$21 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