Read my avove reply. Only the blockchain is the same. The purpose, phylosophy is different. Many "altcoins" are not coins rather than tokens. E.g. Ethereumnis a completely different layer 1 infrastructure with the smart contracts built in the network. ADA is mainly for agriculture, Stellar Lumems is mainly for transportation (see IBM-Maersk solution to track all containers), Ripple is to replace SWIFT, Gaming tokens for gamers (to buy gadgets, ammo, armor, other "NFT"'s), and so on. Of course the first memecoins were just for fun (Doge) or pranking -/as a definitive Ponzi scheme prank, named Ponzicoin.

And there are/were scams e.g. the former Onecoin.