- Virtual Boy, Atari Lynx,
Hardware:
- AMD Interwave. practically ruined Gravis and left us with years of Creative gobbling up any competitor i.e. Ensoniq, Aureal... FFS we had to wait for VIA to make something competitive to Creative's offerings, outside of 3-ish beautiful Cirrus Logic 4624/4630 cards, before the Envy24 became a thing.
- Speaking of Cirrus Logic, The Laguna CL-GD546X series of chips; those things used RDRAM in the mid-90s and it contributed to Cirrus exiting the video market.
- Speaking of Creative, the 3D Blaster VLB. They exist, (heck IDEK if the original rebel moon came any other way,) but they are rare as hell which means they probably flopped hard.
- (Kinda) the Matrox M3d (and the VideoLogic counterpart). It wasn't a terrible product in and of itself but a Riva 128 was faster (if uglier) for most cases and gave you 2D as well, and they came out around the same time. [0]
- Most 'cartridge disk' drives aside from the Zip[1]. You can possibly throw SuperDisk/HiFD into this category too.
- Intel i820 Chipset (It's 1999!). I'm not referring to the 'lemon' aspect (i.e. when an MTH was used for SDRAM, the RDRAM was reliable... AFAIK with two slots instead of 3) but in general there was almost zero uptake due to the cost of RDRAM and Intel's recalcitrance led to both AMD gaining ground as well as VIA/SiS getting opportunities to be more competitive in the chipset space (SiS 630 was cheaper than 810E and just as good for normal users, Via's Apollo Pro 133A both supported 133Mhz FSB and gave an AGP slot, as well as IDE corruption with an SBLive... I think i815 was 4-6 months after VIA stuff was selling, and remember back then 6 months was an eternity...)
Also I should note that the Saturn was mostly a flop in the US (Can't speak for EU.) but in Japan it held up well thanks to native publishers, the Saturn had a lot of great 2D games we never saw here, (thanks to the same guy that ironically caused the relative dearth of good RPGs for the PS1 before he moved from Sony to Sega...) also the ability to play CD+G (gotta have that karaoke) and I think? it could do VCDs which were bigger over there... all that stuff helped a lot and the Saturn outsold there till around 1997 IIRC.
[0] - That said, wow, remember when 3d processors didn't even need a heatsink? I feel old...
[1] - Zip had reliability problems, but certainly was not a flop.