IPFS is described as 'Global, versioned, peer-to-peer filesystem. It combines ideas from Git, BitTorrent, Kademlia, SFS, and the web. It is like a single bittorrent swarm, exchanging git objects. IPFS provides an interface as simple as the HTTP web, but with permanence built in' and is a very popular File Sync tool in the file sharing category. There are more than 50 alternatives to IPFS for a variety of platforms, including Windows, Linux, Mac, Web-based and Self-Hosted apps. The best IPFS alternative is I2P, which is both free and Open Source. Other great apps like IPFS are Hyphanet, ZeroNet, Spideroak One Backup and GNUnet.
I2P is more about anonymity, whereas IPFS isnt inherently build for that use-case. I2P is a darkweb of sorts, ipfs is more about file sharing.