Students can collaborate with others worldwide (over 2 million mappers) to create a free and open digital map of the world.  Students can reflect on and influce how their community is represented on a global map while gaining mapping and digital skills. 

iEARN allows educators to design their own or join a collaborative international project (there are over 200 to browse).  It is flexible enough to be incorported into any curriculum.  They also have a curriculum integration toolkit that aligns with Common Core Standards. 

Epals has been around for a while.  The platform provides some support to educators as they collaborate with another teacher internationally to create a classroom email exchange.  There is flexiblity to create something to fit your needs.  Having all the email correspondance pass through the epals site allows the educator to monitor student correspondence.  A challenge I had with ePals is finding and maintaining a relationship with another educator abroad, interest might wan and when things get busy your project may not be a priority.  There isn't much you can do if your partner teacher stops responding to your emails.  That being said I once worked with a fabulous English teacher in Russia and was able to craft an excellent cross-cultural experience for my Cold War through Space students.

US and MENA (Middle East and North Africa) classrooms partner to develop global competencies.  The IB World Religions students participate in this program during the first half of the course.  Students gain international meeting faciliation skills as they plan and facilitate 4 real time video conferences with their partner school. 

High school classrooms in Qatar and the U.S. are paired to learn about enivronmental issues.  Students gain global competencies as they collaborate using technology.

Italki is a global language learning platform that connects language learners, tutors and teachers.  I have had Lily give short lessons to my 9th grade World History class on the development of Mandarin during a unit on early civilizations.  She also has given specific lessons to my IB World Religions students on the nuances of translations of the Tao Te Ching.  As an educator I have found this site to be helpful when I want to connect with someone in another country, but I don't know anyone who lives there.  For example, when I was preparing to travel to Morocco as part of the IREX TGC fellowship I found a female teacher in Morocco who was able to give me advice on which language to focus on reviewing (French or Moroccan Arabic) as well as answer a few questions.  Another interesting feature are the free language exchanges between students.  Students can seek each other out across the globe to practice speaking or answers questions.