Xfce4-time-out-plugin makes it possible to take periodical breaks from the computer at user-configurable intervals. During breaks it locks your screen for a period specified by the user. It optionally allows you to postpone breaks for a certain time.
Xfce4-time-out-plugin documentation
See NEWS for details on changes and fixes made in the current release.
Xfce4-time-out-plugin source code
Xfce4-time-out-plugin archive or Xfce4-time-out-plugin tags
From source code repository:
% cd xfce4-time-out-plugin
% ./autogen.sh
% make
% make install
From release tarball:
% tar xf xfce4-time-out-plugin-<version>.tar.bz2
% cd xfce4-time-out-plugin-<version>
% ./configure
% make
% make install
Visit the reporting bugs page to view currently open bug reports and instructions on reporting new bugs or submitting bugfixes.