Calculator to graph equations

[tc101]

Is there some free open source calculator that can be used to graph Quadratic equations, trig functions and so on, kind of like the TI-83 or other calculators used in math classes?

[erginemr]

You should check out Qalculate:
http://qalculate.sourceforge.net/screenshots.html

[[woodstock]]

If it is just about plotting graphs, you could try "Lybniz", too. It is in the repositories.

[mrkilgoretrout]

Gnuplot is very easy to use as well. For example
Plot x**2
Will give you your parabola, etc...