You really should take advantage of the free until August 2015 license that is currently being offered with a fresh download TinkerPlots. Would that it was freely available in perpetuity without condition, but a year of tinkering is nice.
If you are a middle school teacher, then this is designed for you and yours. If, like me, you are not, you may find it fun to play with anyway. Here is something I was playing with recently:
An elementary school number sense activity
In the JUMP math curriculum for grades 3 and 4, there are lessons where students investigate the patterns formed when multiples of a number are written in a 3 or 4 column grid. After some number talk students play a game where some entries in the table are covered up or erased, and students have to identify the blanked out value and state the corresponding multiplication fact.
An interactive game like this is easy to make in TP - in the above screen shot multiples of 3 are arranged in a 3 column table. When a student provides an answer, clicking on the square will cause the answer to be highlighted in the number line. For fun, I added an additional plot that shows where the number would lie in a 10 point circle diagram (which students may have already been using to help remember and identify patterns in multiples). The multiple used and the number of columns displayed can be adjusted using sliders, and the "blanks" can be re-randomized by clicking Ctrl-Y. The file is here.
Update: John Mighton gives an overview of the kind of lesson that uses charts like these in JUMPs guided discovery method here.