One aspect of digital citizenship is empathy. When one has empathy for others, one is more likely to be tolerant, understanding, and kind. Therefore, building empathy for others, especially those in a different culture and location, can be a great way to increase a sense of global citizenship.
In the past, it's been cumbersome to find students in other cultures and locations. Fortunately, with today's technology, we can. One such service is PenPal Schools. This service provides a safe online environment for students and classrooms to connect with each other. All messages can be monitored by teachers.
They even offer a PBL curriculum that is aligned to Common Core, TEKS, and IB. On their site is a list of projects that can be filtered by project length, time commitment, student age, and subject. Projects include learning about other cultures, multiplication & division, meteorology, cartography, robotics, and geography.
This service does come with a price tag, however. They try to help you with grant opportunities in case their price is prohibitive for you.