Bitshares (also a graphene chain) Hashed Time Lock Contracts (HTLC):
https://www.jmjatlanta.com/index.php/2018/09/27/bitshares-and-hashed-time-lock-contracts-htlc/
Interledger Protocol (ILP):
https://whaleshares.io/@christopher/bitshares-and-interledger-ilp-summit-summary-for-the-bitshares-community
IBC might not be that far off for Hive as well, just need to connect the right devs for that which Agorise would be happy to help with.