PQcalc
PQcalc is an online calculator for sciences learners. You can try it out here.
For beginning students,
this version gives a bit more feedback. To learn how to use the tool, click on the help button
below the input box of PQcalc (this will fill the input box with some command, which you can then try by hitting
the go button). For a quick tour of the user interface, watch the
video.
For a more detailed overview of the capabilities, take a look at the
manual. The source code is available at github.