Microsoft is expanding its family of enterprise-search products with a new offering: Microsoft Search Server 2008 Express, which essentially takes the search functionality from its SharePoint Server product but is offered as a free download.

Microsoft hopes to garner some attention by offering features that would otherwise be available only in commercial products, such as no limit on the number of documents that can be indexed. But unlike paid alternatives, Search Server 2008 Express is limited to run on a single box. The effort will take Microsoft up against Google’s entry-level Mini and mid-level Search Appliance, both of which wrap Google search software in a dedicated server. Another key competitor will be IBM, which late last year joined forces with Yahoo to produce a free search product, IBM Omnifind Yahoo Edition.

The release candidate for Search Server 2008 Express is available for download here, with final availability expected in early 2008.