earlyoom (the early out-of-memory daemon)

The Linux kernel's OOM-killer generally has a bad reputation among
Linux users. One may have to sit in front of an unresponsive system,
listening to the grinding disk for minutes, and press the reset
button to quickly get back to what one was doing after running out of
patience.

earlyoom is a userspace daemon that can be triggered earlier than the
kernel's OOM-killer. It checks the amount of available memory and free
swap up to 10 times a second (less often if there is a lot of free
memory). By default if both are below 10%, it will kill the largest
process (highest oom_score). The percentage value is configurable via
command line arguments.

To enable it, put this line in your rc.local after running chmod +x on
/etc/rc.d/rc.earlyoom:

if [ -x /etc/rc.d/rc.earlyoom ]; then
    /etc/rc.d/rc.earlyoom start
fi

...and to have it exit at shutdown, put this in your rc.local_shutdown:

if [ -x /etc/rc.d/rc.earlyoom ]; then
    /etc/rc.d/rc.earlyoom stop
fi

A log file for it is kept at /var/log/earlyoom.log, and earlyoom can
be configured by modifying /etc/default/earlyoom.