Geometer’s Sketchpad is a useful tool for visualizing euclidean constructs, as well as a multitude of other things.  However, it is also expensive, with a new license running around $70, and renewals at $50.

Luckily, there is an open source version of the software called GeoGebra.
There are a number of links to help you get started with this free software:     Here you can download the software for installation on your computer (this is how I use the program).      Here, one may tour the GeoGebra software via a well put together tutorial.

That’ s all I have for the moment.  A quick Google search for GeoGebra will pull up all kinds of reference materials