8-Track, whose inventor also founded Learjet, challenged reel - to - reel and minicassettes for the audio - on - the go market. While most critics agreed 8-tracks had better sound quality, they were bulky and their market share fell to just a niche market.
After the 1.44MB floppy, numerous "superfloppy" formats came out. Iomega's Zip drive held the largest market share, but then rewritable C Ds and portable memory sticks came out....
DVD-R vs DVD R vs DVD-RAM: these formats were so similar, customers got them mixed up, so now most writers do both R and -R. The market is about 60% -R / -RW and 40% R / RW with only single digits for -RAM.
Bionicle and Mega Blox's Blok Bots and Neo Shifters. Hot Wheels and Matchbox anyone?