I saw this in a PowerPoint presentation as the title of a list of ways for teams of employees to communicate with one another during a weekend software-launch project.

Problem:
The plural form of medium for most of its definitions, including the one used in this title, is not “mediums”.

Explanation:
One of the definitions of “medium” is psychic (someone who claims to be able to communicate with the dead or predict the future).

The definition of “medium” that the title writer had in mind is means of communication. The title writer probably put the word “Communication” at the start of title to emphasize that she was using this particular definition.

The plural form of “medium” when it means psychic is “mediums”; the plural form of “medium” for other definitions, such as means of communication, is “media” (not “mediums”).

Solution:
“Communication media:”