Satellaview

Even most hardcore Nintendo fans don't know what the Satellaview is, never mind having actually played one. This is partly due to the combination of No Export for You and one of the more bizarre examples of Keep Circulating the Tapes in video game history.

Some time after the SNESCDROM was canned (cue Epileptic Trees about a Plan B), Nintendo signed up on a deal with St.GIGA (a now-defunct Japanese Satellite Radio company) to have a Super Famicom add-on which allowed users to both download software and stream Satellite Radio. This setup was eventually released in 1995 as a special-mail-order, subscription-based service.

The add-on had a bit of an unusual setup — downloads were broadcast in timeslots much like radio and TV shows. Some downloads were expected things like old SNES releases, demos of new games, and original game content. On the stranger side were some downloadable magazines full of Japanese celebrities drawing Squicky pictures of Mario with an Asian face. While snagging all this content, the Satellite Radio would stream various programs which attempted to tailor to the gamers' tastes, and were hosted by J-Pop Idols and comedians.

Eventually the bright idea came around to have a game set-up to play alongside the Satellite Radio playing unique game-specific audio, and thus the Satellaview's most remarkable and famous accomplishment was noted: the SoundLink games, which did just that, using the functionality to bring new stories for some of the Super Famicom's most prominent titles, like The Legend of Zelda and Fire Emblem: Mystery of the Emblem.

Unfortunately, most of the Satellaview's unique features came with "catches" that would lead many to turn "BS" into an Incredibly Lame Pun (for reference, the original meaning is a generic Japanese term for "Broadcasting Satellite", tagged onto various programs transferred via satellite). The Satellaview is one of the first notable examples of DRM used in console gaming — many games were set up to have limited boot-ups, and many others were only allowed to play at the specific broadcast time. Much of the contents are presumed to be Lost Forever because of the limitations of people merely being able to download data.

Well, at least more of it was recovered than the Sega Channel, huh?

Much of the actual capabilities of the Satellaview were unknown to the non-Japanese for the longest time, leading to various rumors and misinformation. Fortunately, quite a lot of the issues can be cleared up by watching various video archivals of gameplay from the original broadcasts on Nico Nico Douga. The Satellablog is a blog devoted to recovering and archiving footage of and information about the Satellaview, and is perhaps the most complete English-language resource on the Satellaview there is; it's related to a project which aims to eventually restore as much functionality as possible to Satellaview emulation, possibly including SoundLink transmission. The Other Wiki has some very in-depth information on the technical side of the system.

To date, the only Satellaview titles to be rereleased in any form are the four BS Fire Emblem chapters, which were remade as bonus content in Fire Emblem: New Mystery of the Emblem; the remakes do not incorporate the voice acting of the originals.

Games

The Satellaview's user interface is presented as a game itself, titled BS-X: The Story of The Town Whose Name Has Been Stolen. The system's content and options menus were accessed by visiting buildings around the town, which all looks rather reminsicent of EarthBound.
Anything with "BS" tagged in the front or at the end is a SoundLink title, where the game was played alongside radio-streamed audio; these include BS F-Zero, BS Super Mario USA, BS Super Mario Collection, BS Fire Emblem, BS Marvelous, BS Tantei Club...
The most notable of these is probably the first BS Zelda, which is a a remake/remixing of the NES Zelda. This was followed up by a Mission Pack Sequel where the overworld was changed, and then by Inishie no Sekiban, which is more like a Mission Pack Sequel for A Link to The Past.
Radical Dreamers, Koi ha Balance, and Treasure Conflix, three Square Soft original releases.
Satella-Q, perhaps one of the most obscure Mario spinoff games ever — a J-Poppy quiz game starring Toad.
Excitebike: BunBun Mario Battle Stadium, a remake of the NES Excitebike with Mario characters and Mario Kart 64 voice effects.
Sutte Hakkun
Kirby no Omacha Hako, a series of mini-games starring Kirby.
Special variants of games, such as Wario's Woods, with celebrity cameos or other changes.
Various things not listed here.