You don't need a full sized computer to be connected 24/7, Just grab a Raspberry PI or any (sometimes even cheaper and less power hungry) equivalent, flash the smallest OS of your choice that does what you want: serving videos and files, seeding torrents, hosting a node of your favorite communications platform, etc. You can keep the system on SD then use two USB drives for data, the second rsynced to the first, so you have some sort of redundancy without RAID. Total cost less than $100, possibly a lot less if you already have some parts (used hard drives and USB enclosures, SD card, etc). SSD drives would be overkill and more costly.
If well tuned (drives spinning down when not used after a safe limit, say 2 hours, efficient CPU throttling, etc) It could draw less energy than the smallest lamp in our house: totally sustainable.
About the software, I have a dream (tm): NNTP expanded so that it can be integrated with other services, include small binaries natively, or magnet links when above a certain size, the torrent being automatically created, seeded and linked by the originating user's client, employ enough security to become troll/vandal proof, etc. The infrastructure is already here, but the protocol is too tied to the limitations of the Internet in the 70s and 80s and takes for granted that everyone is a gentleman, which makes it hardly usable today.
About the software, I have a dream (tm): NNTP expanded so that it can be integrated with other services, include small binaries natively, or magnet links when above a certain size, the torrent being automatically created, seeded and linked by the originating user's client, employ enough security to become troll/vandal proof, etc. The infrastructure is already here, but the protocol is too tied to the limitations of the Internet in the 70s and 80s and takes for granted that everyone is a gentleman, which makes it hardly usable today.