Hyper-V. Accordingly, the company is running a time-limited promotion : switch from VMware to Hyper-V and the company will give you "free" licenses to Windows Server Datacenter.
To help persuade companies to switch, Microsoft has offered a TCO calculator to show off the big savings (Microsoft hopes) that can be had from making the switch.
The company is offering a similar promotion for companies that are willing to switch from Oracle to SQL Server 2016 ; "free" licenses with purchase of Software Assurance.
That Microsoft is gunning for VMware customers is no big surprise; VMware is the market leader here, with Hyper-V a relative latecomer to the scene.