VMware CEO Paul Maritz has said that the company has considered open-sourcing its hypervisor, and supporting rival virtualisation tools made by competitors.

He didn't give any indication about if or when those changes would be implemented, but did say during a public Q&A at VMworld in Las Vegas that "we have thought about whether we want to open source ESX,"

Maritz, who recently took over the CEO role previously held by VMware co-founder Diane Greene, noted that he has already decided to offer VMware's basic hypervisor for free. He expressed admiration for how the open source model encourages participation by anyone regardless of where they are located, but he didn't say whether VMware will actually open source ESX.

Maritz also addressed questions about whether VMware should support multiple hypervisors, as some customers want to use virtualisation technology from more than one vendor.

Microsoft System Center is capable of managing both Microsoft's own Hyper-V technology and VMware virtual servers, but as of today VMware only manages its own virtualisation products.

Maritz said VMware often gets asked whether it will support other hypervisors, such as the open source Xen software.

"At this point in time, we don't support hypervisors other than our own, but it is something we look at," Maritz said. "As soon as we've got our framework in full execution we'll come back and look at that question."

Maritz, a former Microsoft executive, said VMware is entering a new phase because of competition from vendors such as Microsoft.

"Clearly we have competitive challenges," Maritz said. VMware "has been the huge beneficiary of essentially being the only game in town."

Maritz said it will "take a while" for Microsoft to build up its own virtualisation technology but that it still presents a threat to VMware.

"We can never count [Microsoft] out," he said. "They have a lot of resources. We can't rest on our laurels."