You can get documentation on syslinux/isolinux/memdisk here
. These are open-source tools developed by H. Peter Anvin, with a huge following.
syslinux and isolinux are the same boot loaders for different media. syslinux is for floppies/USB memory sticks etc., while isolinux is for CD/DVD, but they understand the same .cfg files.
memdisk is a RAM-based floppy disk emulator.
The syslinux directory is required for booting UBCD from USB memory sticks (see tools\ubcd2usbubcd2usb.bat), while isolinux directory is required for booting UBCD from CD/DVD (see tools\ubcd2usbubcd2iso.bat), but they use the same set of .cfg files under "menus".