Vault vs HCP Vault

Hii Everyone
I have one question regarding the difference between Vault and HCP Vault.
I earlier read that the two are not different in the functionalities they provide. But then i discovered that namespace, tranform and a few more plugins are not present in the free version of vault.
Everywhere its written that Namespace and others is a part of Vault Enterprise. so i though it is regarding feature and not subscription.
Can anybody kindly help me with the difference of functionalities that we get between the two?