ulagen.py is a short python script to generate an IPv6 unique local address as per the pseudo-random algorithm defined in RFC 4193. Run it without any arguments. For example:

% ./ulagen.py
Prefix:       fdf3:5237:bf63::/48
First subnet: fdf3:5237:bf63::/64
Last subnet:  fdf3:5237:bf63:ffff::/64