Beatmania IIDX is 7+1 and is by far the most popular 8k rhythm game. In beatmania, the large lane is for scratch notes where you have to physically spin a platter to register a note, as if you were scratching a vinyl record.
I personally cant think of any game that is symmetrical 8k. Not saying there arent any, just that I cant recall any.
Looking for mods for my mania map Minori Chihara - Kyoukai no Kanata (TV Size). Need some tips on how to improve in osu!mania? Try reading our guide and map suggestions! Need some tips on how to map in osu!mania better? Try reading this guide! Looking for the o2jam skin I use? This folder has it and a few other o!m skins! Message me if this link doesn't work, and I will update it.
1key of 7+1 style is expressing a special sound. It's mostly for crash sound / beep / vocal rhythm. And yeah that style is from IIDX and BMS as what Bobbias said.