There is a free FrontPage extensions clone being developed by Mrs. Brisby, which is just a single CGI script. You can find it at http://www.nimh.org/fpse.shtml.

This software is not complete at the time of this writing and may not implement all the features that the FrontPage client requires.

You might notice when you login to Microsoft's ftp server that in the FrontPage extension directory there is another directory containing the development 5.0 version of the extensions.

WebDAV is a more standardized and open protocol that is looking to replace FrontPage. WebDAV is something that was originally developed at Microsoft but has spun off a bit. I think that most of the office products are somewhat WebDAV enabled. Check out Greg Stein's WebDAV presentation at ApacheCon 2001 for more information.