ipxe is an open-source implementation of PXE. It is a network boot firmware. This helps to boot from network. Licensed under GNU GPL. Additional features are like boot from a web server via HTTP, boot from an iSCSI SAN.
iPXE (formerly gPXE, formerly Etherboot) is an open-source Preboot Execution Environment (PXE) implementation and bootloader. It can be used to enable computers without built-in PXE support to boot from the network, or to extend an existing PXE implementation with support for additional protocols. While traditional PXE clients use TFTP to transfer data, iPXE adds the ability to retrieve data through other protocols like HTTP, iSCSI, ATA over Ethernet (AoE), and Fibre Channel over Ethernet (FCoE), and can work with Wi-Fi rather than requiring a wired connection.
More info on http://ipxe.org/
