Electronic Toolbox
with the following tools:
1) PI and T attenuator
2) Power and voltage converter
3) Parallel LCR impedance/resonance
4) Series LCR impedance/resonance
5) Inductor impedance
6) Capacitance impedance
7) Ohm's Law
8) Radio equation calculator (1-way path loss)
9) Air Core Inductor Inductance Calculator
10)Capacitor impedance
11)Noise floor
12)Amplifier cascade (NF, Gain, P1db, OIP2, OIP3)
13)Low Pass filter
14)High Pass filter
15)Helical antenna
16)Band Pass filter
17)Peak to RMS (peak, RMS, average, CF)
18)Mixer harmonics
Also checkout the RF & Microwave Toolbox which has all the tools of the Electronic Toolbox and the RF & Microwave tools.
Please let me know if there are electronic related tools that you would like to be added.