I have seen this BU being spewed on the forum lately in full force but can not find out what it is.
BitcoinCore devs or something else. At first I thought it was something like Butterfly labs but then thought that didn't make much sense with all the talk concerning what they do will effect the ETF to come in March.
I actually did a search typing in BU in the search field here but my efforts were for nothing but miner threads.

Ah ok Bitcoin unlimited.

I saw it on a torrent site and just saw the size of it and decided not to touch it.
Was just a clone of bitcoin core.