Submitting this re: the recent discussion about PGP alternatives. It seems right in line with the types of tools that were being suggested for replacing specific use cases of PGP. Written by Tony Arcieri, who is well-regarded in the cryptography community.
"However, it also provides seekability, allowing individual files within the archive to be decrypted, in addition to seeking within those files"; I don't it's implemented yet, but the protocol seems to have that capability.