When language evolves, our use of medium and media have separated and expanded considerably from their latin origins. The vast majority of people when using media in the meaning of something to transport information, use it as a singular uncountable/mass noun: 'The media are (Edit: I've just realised this is plural, doh
, but 'is' also works here and what is countable is the number of types of media, not the number of e.g. journalists. If it's only the papers outside then it's usually an 'is') waiting outside his house', 'social media is harming our children' etc. Medium in such a sense typically refers to a single type, not a single item. E.g. TV is a medium, films are a medium, "Mr. Smith communicated his ideas via the medium of film", no one ever refers to a single paper or program or film as 'a medium'. Or perhaps 'how many media does the newsagent stock?' nonsense sentence!
The actual latin word medium means either middle or community. The sense of it expanding to something for something else to travel through is very much an english evolution, most likely first in science, then for information. The attachment to latin pluralisation is rather pointless. It's also incorrect from a latin perspective which. If you want to go full latin, media is only the plural in specific cases, mediis and mediorum would also need to be used. A blanket use of the nominative is daft.
There are other borrowed latin words that more or less far along this line of evolution. Take stamina and agenda. Ever heard anyone asking 'how many agenda are left in a meeting?', 'Can we quickly cover the rest of these agenda? I need to get the 15:00 train.'
The most irksome for me is probably 'these data'. Data, a word that literally in latin means 'given' (dare = to give, do = I give). Like media, our current usage seems to have fallen through from science where writers already started to warp the meanings while writing in latin and then kept words over, essentially as jargon, when they moved to using modern languages. When asked how many data they have, the answer, of course, comes back in the form of how much.
As for forums, pianos. Used to do much with computer games, not so much now.