Exec-shield
Exec-shield is a kernel patch enabling new security features in the Linux operating system. Exec-shield provides protection against stack, buffer overflows, and other exploits relying on overwriting data and inserting code into those structures.
The patch additionally increases the difficulty of inserting and executing "shell code" rendering most exploits useless. No application recompilation is necessary to fully utilize exec-shield, although some applications (mono, wine, xemacs) are not fully compatible.