fget supports downloading a single URL (the first argument on the command line) from an FTP or HTTP server. fget supports IPv4 and IPv6 (the IPv6 URL format for IP numbers is http://[::1]:80/file.tar.gz) transport. You can set the INTERFACE environment variable to the name of the network interface ("eth0") to use IPv6 link-local addresses. This program can acces URL's with username and password like http://bob:email@example.com/file.tar.gz Files are always written to stdout.
fget is meant for boot and rescue disks, so small size is the most important feature. It can be linked against diet libc and you can disable the built-in DNS routines to make the binary even smaller. On my x86-linux box, the diet libc statically linked fget binary without DNS weighs about 24k (update! dietlibc 0.5 reduces the size to 13k!)