GeoGebra is a free and open-source graphic calculator for students, teachers.
GeoGebra is a dynamic math software can be used by students, teachers and schools. It provides easy to use interface for drawing with all types of graph drawing methods.
GeoGebra also provides different types of views of mathematical objects e.g. Algebra view, Graphics view, Spreadsheet view, CAS view, 3D Graphics View and probability Calculator View.
This software comes with a Web interface as well which you can try out without installing. For portable devices, it comes with mobile and tab installer as well. You can find the installers in official download page.
The learning manual for Geogebra is quite extensive and there are separate learning materials available for new users and advanced users. It also comes with a Tube Site a.k.a GeoGebra Tube which contains user uploaded graphs which also can be downloaded in various formats. GeoGebra graphs can also be embedded as applets in HTML web pages.
You can take a look at the tutorial videos like below in official YouTube channel

How to Install GeoGebra in Ubuntu, Linux Mint
Grab the official deb files from below links and install:
Download GeoGebra 64 bit Download GeoGebra 32 bit
Or, run below commands to install.
64 bit
wget http://www.geogebra.net/linux/pool/main/g/geogebra5/geogebra5_5.0.231.0-46890_amd64.deb sudo dpkg -i geogebra5_5.0.231.0-46890_amd64.deb
32 bit
wget http://www.geogebra.net/linux/pool/main/g/geogebra5/geogebra5_5.0.231.0-46890_i386.deb sudo dpkg -i geogebra5_5.0.231.0-46890_i386.deb
After installation, find GeoGebra under Application menu / Search in Dash.
Drop a comment using comments box below if you face any problems using GeoGebra or any opinions.