It doesn't appear to be open source, but IBM offers Watson IoT with Blockchain as a platform for secure private blockchains for IoT services:
IBM Watson IoT Platform enables IoT devices to send data to private blockchain ledgers for inclusion in shared transactions with tamper-resistant records. Blockchain’s distributed replication allows your business partners to access and supply IoT data without the need for central control and management.
In reality, what IBM hopes to achieve with this is:
records that should be impossible to modify (just like Bitcoin's ledger)
decentralization, which should (in theory) remove the need for data servers for the business
'smart contracts', which can automatically perform actions if a criterion is met.
The example they give on their website (near the 'Play' button in their 'Overview' section) is a smart contract which would detect if a package overheats and automatically charge the organisation responsible at each stage. For example, if a package overheated during shipping, the smart contract could automatically assign responsibility to the shipping company or highlight a package for inspection to check that it's still OK.
However, there's still some things to be sceptical about. As noted by Tractica:
One of the details that IBM talked about during the briefing was related to the implementation of blockchain on low-power devices. With the processing of blockchain being extremely challenging on these low-power devices, the blockchain processing is performed in the cloud.
So, in theory, all the processing gets done on the device itself, removing the need for the centralised server... But in reality, the overhead of the blockchain (e.g. the cryptography involved, which is always a problem for low-power devices) forces IBM to provide a cloud solution anyway. It would certainly be worth investigating this further before deciding if this is a good solution—if cloud access is required anyway, a centralised server might make a lot more sense—and save a lot of money—by avoiding the requirement for all your devices to run the cryptography you need for the blockchain.