Are there any free online and/or offline alternatives to the step-by-step-solution feature of Wolfram|Alpha Pro?
This feature is able to display step-by-step-solutions of a wide variety of algebra problems, as shown in the example screenshot below.
Another great alternative is: https://www.symbolab.com/
It has also got a premium area, but its step-by-step solutions are free.
One good alternative is: http://gamma.sympy.org/
It doesn't show steps for factoring but it does show steps for more complicated things in Calculus like derivatives and integrals.
Another free option is photomath. Not as advanced as WolframAlpha, but may be suitable. It is available for Android.
Open Omnia is an alternative to Wolfram Alpha Pro and Symbolab. Disclaimer: I am the developer.
You can find the web application here: https://openomnia.com and the android app here: https://play.google.com/store/apps/details?id=com.openomnia.openomnia
Feel free to try it out.
I've just found fxSolver... It doesn't seem to show all the workings, but it does provide help and background on the inputs, and allows plotting.