I use Google Classroom to post classroom notes, assignments, important links, and resources for each of my classes.  Students are given a classroom code at the beginning of each year to access the site.  The Google Classroom app is available, for free, for multiple devices and platforms.

Desmos is a free online graphing program with an easy to use interface.  Students can create a Desmos profile using their school Google account allowing them to save and share their mathematical creations.  I also use Desmos Activity Builder as a way to create interactive lesson with the Desmos program.  Desmos also provides a free app on nearly every device and platform.

GeoGebra allows students to explore complex concepts in mathematics via a powerful educational tool.  The program goes beyond what a traditional calculator can offer and also features a Geometry mode for geometric constructions and analysis.  GeoGebra has a free app for devices and allows students to create a profile with their school Google accounts.

I use my @kmtobe account on Twitter to post interesting happenings from my classes and professional discussions.  Feel free to add to my list of followers!

My YouTube channel highlights videos that my students have made as part of Project I.C.E. (Innovate, Create, and Explore) and a handful of videos that I use for classroom instruction.