zkLedger is a design for a ledger which has private transactions, but supports provably-correct queries over the ledger.
Maybe you'd like to run the tests:
cd $GOPATH/src/github.com/mit-dci/zkledger
go test
Or, run a local experiment with a few banks, a single-server ledger, and an auditor:
cd cmd/setup
go build
./setup -t simple1
(You can add -debug to get a lot of timing information and other debug output)