Geogebra is such a necessary tool for students especially in Geometry.
I use geogebra in geometry to explore pretty much every concept. I love that its more user friendly and now available via ipad. I also love that it's in the chrome app store. In the past, it was a bit more clunky but the new version is so user friendly that kids can dig right in and learn. As a free dynamic geometry tool, it has totally impacted my classroom as it made geometry more than just images on a worksheet but applications that students could play with.
How I Use It