We made
https://btc.usespiral.com, which lets you look up the balance and recent transactions of any Bitcoin address, without revealing to the server which addresses you look up.
We use homomorphic encryption to process your query without being able to learn anything about it. The point is to let you keep your identity (IP address) isolated from your money. We are scaling up this website into a production API, and adding support for more detailed transaction info and other blockchains.
An academic paper about the scheme underlying our site is available here:
https://eprint.iacr.org/2022/368.pdf. We're working on a whitepaper about our Bitcoin address lookup system in particular.
If you have feedback or ideas on what we should work on next, let us know! We are thinking of trying to generalize this into a "private RPC" protocol, but we're not sure how valuable that is.