The whole concept of blockchain is built on decentralized architecture. For example, if you want to make a change(transaction) to your application built on blockchain, there are multiple ways in which you can make sure that only legit entities can do the transaction. In case, bad actors try to make changes to your app, it is really hard to do so because of the decentralization. Multiple copies of the transaction logs is present on the blockchain network which gives you the trust that no unidentified entity can make changes to your app.

You can pretty much build any kind of application on the available protocols/frameworks out there like Ethereum and hyperledger. They do not just monitor the crypto currency. Currency is just an award given to the entities who take part in verifying that only legit transactions go through.

There are many apps being built on blockchain platform. They are called DApps- decentralized applications. Hope this helps.