Choosing External Tools for Learning & Communicating
Free of charge (for anyone, not just you): We avoid tools that P2PU might get sponsorship for, but that others could not use.
Open as in open source and standards: This is better than free of charge, because it gives us and you even more control and assurance that the tool will always be available (free of charge might not be free of charge at some point).
Other things to keep in mind:
Learning aspects: If there are particular learning objectives, or styles that you have for the course - choose tools that support them.
Technical aspects: Not everyone can evaluate the technical quality of a tool, but it's worth thinking about stability (is the tool reliable and robust) and scalability (if you have 70 people in your course, will the tool support a group that large?). Most tools have been used by other course organizers before so ask about other peoples' experiences before making a final choice if you are not sure.
Less is more: Offering too many different tools confuses users. Keep it simple and provide links to tutorials or give users basic introductions to the tools you will use.