Can someone please explain which client uses these different forks or codebase? Does the bitcoin core client use these? I don't see anything in bitcoin.org about these different block chains.
they are not different chains
they are the same network. just different brands of software.
the issue is that the network is no longer decentralised and diverse, the "core" brand only want to publicise their brand and their affiliates brands. and treat anything not endorsed by them as something they should reck, dismiss, create fake stories about how they are altcoins.
core have slowly but surely wanted to centralise themselves as the sole brand of bitcoin. literally naming themselves "core" (centre of the earth)
the other brands have not set deadlines nor advocated to destroy the method of securing the chain (PoW). but core is doing all it can to try keeping its stronghold grip of being the centralised titanic managers of bitcoin.
which all go against the ethos of why bitcoin was even invented. they even wanted to rewrite the whitepaper that inspired the invention of bitcoin, so you wont find anything that opposes "core" on bitcoin.org. because bitcoin.org is controlled by the same core group
