MediaMaster Server is a webDAV server for your Mac. WebDAV is a protocol that lets you access files on a computer over the Internet. Other protocols that are often used instead of WebDAV are FTP and SFTP. In this case, the WebDAV protocol is used by MediaMaster Server to let you access your files from any device that can interpret the protocol.
On the iOS App Store, you can download MediaMaster for iPad, which allows you to open and edit files on your Mac.
In my case, I have been using MediaMaster Server to stream my video files to a home theater PC that has XBMC installed on. AFP (another protocol) was giving me trouble, and Mac OS X Lion's SMB implementation seems to be broken at the moment, so MediaMaster solved all my problems.
After installing the application, you have to select the directory you want to share, along with the authentication settings that you want to use. You can also choose the port and enable secure HTTP. There is a toggle that turns the server on and off. It is that simple. I am a picky user, so I would like to be able to add more than one folder to the list of shared folders, and I would love a setting that would launch the application when my Mac boots up. Since it is a free application, and a savior, I can't really complain, can I?