FTS is a TFTP supplicant package. It uses a FUSE filesystem in conjunction to your ordinary TFTP service (like atftpd, tftpd, etc.) in order to provide dynamically generated start configurations for certain MAC addresses.
If you have different mechanisms which compete for PXE boot authority, it may be hard to glue all of them together. For that reason, FTS creates a filesystem layer on top of your ordinary (static) tftpboot directory and tries to resolve the requested files within it's modules first - then falling back to your static files.
There are currently modules for OPSI, FAI (LDAP), LTSP5 (LDAP) and Clacks. If you've installed all of them, a booting client will first request a file partly named after it's hardware address (MAC). Every FTS module is asked if it want's to handle the provided MAC address in an unspecific order. The first one which claims to have a proper PXE configuration will provide a virtual file which is then served to the client.