gWakeOnLAN is a small graphical utility that lets you wake up machines using the Wake on LAN (WOL) feature. WOL lets you wake a computer from a low-power state when a network adapter detects a WOL event. Typically, such an event is a specially constructed Ethernet packet, often known as a “magic packet”. When the packet is received, the target machine’s network device (Network Interface Controller or NIC) wakes up the rest of the machine.

Source: LXer – Essential System Tools: gWakeOnLAN – turn machines on through Wake On LAN