Validator S.A.C. (Stand Alone Complex) is a stand-alone, easy to install, version of the W3C's HTML / XHTML Markup Validator for Mac OS X. [...] Validator S.A.C. can validate local files, as well as pages on local web sites. [...] Validator S.A.C. can also be setup as a Web Service, allowing users to validate over the local network.

via Validator S.A.C. - Stand-Alone W3C HTML Validator Application for Mac OS X.