Exec Shield is a project started at Red Hat, Inc in late 2002 with the aim of reducing the risk of worm or other automated remote attacks on Linux systems.
This suppresses many security exploits, such as those stemming from buffer overflows and other techniques relying on overwriting data and inserting code into those structures.
Because of the way Exec Shield works, it is very lightweight; however, it won't fully protect arbitrary virtual memory layouts.
However, in cooperation with the Security-Enhanced Linux project (SELinux), the standard policy for the Fedora Core distribution does prohibit this behavior for most executables, with only a few exceptions for compatibility reasons.
[1][2] Other people involved include Jakub Jelínek, Ulrich Drepper, Richard Henderson and Arjan van de Ven.