Lots of people are using Tendermint. The biggest users would be Hyperledger Burrow (https://github.com/hyperledger/burrow) and our own Ethermint (https://github.com/tendermint/ethermint). We're also working on an SDK for building apps in Golang (github.com/cosmos/cosmos-sdk) but it won't be ready for another month or two. There are a variety of apps built by members of the community, and ABCI servers in different languages - you can see a somewhat up-to-date list here: https://tendermint.com/ecosystem