1Password's format is also documented [1], though I'm not aware of any 3rd party clients to parse/work with it. That's actually a thing I was thinking about writing (I commented about trying to write something in C++14 in another front page thread, this was it)
1Password also uses standard encryption, from the link [1]:
> We use Encrypt-then-MAC authenticated encryption everywhere we use encryption. The MAC is HMAC-SHA256 and encryption is AES-CBC using 256-bit keys. Key derivation is uses PBKDF2-HMAC-SHA512. More detail about these choices will be presented in the relevant sections on key derivation and item encryption.
> In this document we will refer to “blocks of data”. Unless otherwise stated, blocks are the length of AES blocks, 128 bits (16 bytes).
Edit: apparently Github lists [2] four libraries for reading OPVault, one each in Python, Haskell, Go and Ruby