Earlier quoted context omitted.
The one that seems to be gaining the most traction is IPFS[1]. /ipfs/ URLs are content-addressed (like git objects). As long as someone has a copy of the data somewhere on the IPFS network it will continue to be available, and if you manage to get a copy of the content from somewhere else you can try hashing it and make sure it matches. (And if it does you can `ipfs add` it and it will become available again, even if…
I should have added "human readable short persistent url". Like foo.com/xy/github where xy is an identifier as short as possible to avoid collision. And with ipfs you are dependent on the ipfs own domain. To remove domain dependency it would have to be something not based on current DNS system.
No, you might have gotten something wrong here. We (I work at Protocol Labs, I'm part of the development team working on IPFS) are hosting a public gateway you _can_ use but in no way have to use. You can either use your own local gateway, another gateway via IP or accessing the other peers gateways if that's accessible. Nothing is tied to the "ipfs.io" domain.