IPFS is more low-level in terms of that IPFS is a protocol (in reality a collection of protocols) for P2P data transfer. Together with IPLD, you'll get a full suite of protocols and data structures for creating fully distributed P2P applications.
ZeroNet is a application for distributing P2P applications, using Bittorrent for the P2P layer. In theory, ZeroNet could leverage IPFS to get a better and more modular stack for the actual connectivity and transfering.
