The developer image of BizTalk Server 2016 is licensed for free to use in your test and development scenarios.
BizTalk Server 2016 is Microsoft’s latest release of the new hybrid integration software. Users can automate mission critical business processes, leverage support for latest first party platforms and gain newer capabilities within the BizTalk Administration console. With this release, users also have the flexibility to adopt a hybrid approach by choosing to connect to SaaS applications through Azure Logic Apps, or running BizTalk Server on Azure leveraging full support in production environments.
Source: BizTalk Team Blog