A much simpler URL rewriter than mod_rewrite is available at ftp://ftp.apache.org/apache/dist/contrib/modules/mod_uri_remap.c.
The http://www.cs.utah.edu/~ldl/apache-modules/disallow_id/ module prevents access to files owned by specified users or in certain groups. This can, for example, prevent all access to root-owned files.
The module http://www.cs.utah.edu/~ldl/apache-modules/log_peruser/ logs requests for a particular user's pages to a log file in the user's directory.
Both these modules are listed as http://www.cs.utah.edu/~ldl/apache-modules/, along with an enhanced mod_cgi based on the suCGI package.