Tanker developer here. We use libsodium as our underlying cryptographic library. It uses XChacha20/Poly1305 for symmetric encryption, Curve25519 for asymmetric encryption and signature, and Blake2 for hashing.

Why would I use your library over the tried and true https://github.com/dchest/tweetnacl-js ?

TweetNaCl is roughly equivalent to libsodium, on which Tanker builds. Tanker is easier to integrate into your app because it takes care of key sharing, multi-devices, user group managment, etc. These are all things you would have to handle by yourself using just a cryptographic library like TweetNaCl.