Circuit Calculator is an offline interactive design tool for electronics engineers and all electronics enthusiasts.
Convenience visibility and ability to find an optimal solution in minimum time.

80+ analog circuit topologies 30+ electronics calculators 10+ Application Notes Logic Solver.

You can try "Circuit Calculator Demo" before you buy:
https://play.google.com/store/apps/details?id=com.vdv.circuitcalculator.demo

Of course there are vendor's online and offline electronics design tools.
But their tools support only their ICs and what if you don't have access to the Internet or you have only your mobile device with you?
This tool is designed by an engineer for engineers and is able to save you a lot of time!

* Amplifiers;
* Variable Gain Amplifiers;
* Drivers;
* Current Sources and Receivers;
* Lowpass Highpass Bandpass Bandstop Filters;
* Mathematical Operations;
* Power Circuits;
* Others Passive and Active Circuits;
* Reverse: calculation of circuit parameters at known values of its components if it is possible;
* Logic Solver from 2 to 6 inputs;
* Auxiliary tools;
* Application Notes;

You can use Filter Designer to design multistage active filters available in the Google Play Store.
https://play.google.com/store/apps/details?id=com.vdv.filterdesigner