Wikipedia
GPXE
gPXE is an open-source Preboot eXecution Environment (PXE) client firmware implementation and bootloader derived from Etherboot. It can be used to enable computers without built-in PXE support to boot from the network, or to extend an existing client PXE implementation with support for additional protocols. While standard PXE clients use TFTP to transfer data, gPXE client firmware adds the ability to retrieve data through other protocols like HTTP, iSCSI and ATA over Ethernet (AoE), and can work with Wi-Fi rather than requiring a wired connection.
gPXE development ceased in summer 2010, and several projects are migrating or considering migrating to iPXE as a result.