I think the most obvious solution is Cardano-GraphQL. For example, this GraphQL query can be used to call an address with a contract at the UTXO.
Unless you are looking for higher level yet, I believe you should track this proposal or that was successfully funded in Fund5, which I myself happily voted for. Also, since you asked for Rust SDKs specifically, this proposal was funded to update the Rust Serialization Library from the guys at Emurgo to be compatible with the upcoming Alonzo hardfork.
Better yet, a quick glimpse of the successfully funded Fund5 proposals shows pretty decisively that developer tooling (SDKs, APIs) absolutely dominated this funding round, which is exactly what we need right now to grow our ecosystem.
This should be enough to point you in the right direction.