Technically it uses hash chains which blockchains are based on, so it is tangentially related. But IPFS is basically just Git (also using hash chains) with networking addons, no concensus algorithm (none needed).
Take the blockchain out of Etheruem, and you still have a pretty cool deterministic state-transition machine. My understanding of Urbit is very limited, but I believe it has a similar concept of Ethereum without a consensus protocol.
They're probably worth distinguishing somehow for newcomers. They're both transaction logs.
Ethereum is a transaction log with a consensus mechanism. Anyone can append to it. It's a scroll: any group or society can use apps that check the scroll to come to conclusions about the state of their interactions.
Urbit is a transaction log that only the owner can append to. It's a journal: users can safely append to their journal with any app, and their apps can read the whole journal to display data from multiple apps in desirable ways.
Which begs the question, why is Urbit necessary? It would be relatively simple to port Ethereum's consensus protocol to "only a user with key X can sign new blocks" and each block would contain exactly 1 transaction.
Mainly because (as Vitalik says) "the whole Ethereum network has the power of a 1999 cell phone."
Although Urbit (like Ethereum) is precisely defined without dependencies, Urbit is not a consensus computation platform. It's for processing your own data on your own (virtual or physical) machine.
Consensus computing is incredibly inefficient and should be used only where absolutely required. Where consensus is not absolutely required, computing should be localized under the user's control. People often forget to include this component in their designs of the decentralized future. But in fact, Ethereum needs something like Urbit and vice versa.
One way to think about the difference between Ethereum and Urbit: it's like the difference between a superconductor and a regular conductor. On the one hand, superconductors are qualitatively different and fundamentally more powerful. On the other hand, there are no superconductors in your iPhone.
I'd actually put Blockstack in the same category as Ethereum. From a transactional log perspective, it uses the Bitcoin blockchain for consensus on the log and from an application development perspective, you can build apps using Blockstack (gives you naming, auth, and storage).
