Miredo is an Unix daemon program which mostly implements the
"Teredo: Tunneling IPv6 over UDP through NATs" Internet proposed
standard (RFC 4380). It can provide either client or relay
functionality. A separate program, miredo-server is also included in
the package; it consists of a Teredo server.

Miredo can be used to provide IPv6 connectivity to users behind NAT
which do not support IPv6, and not even proto-41 forwarding. For this
to work, users need to have a Teredo client running on their system.
That can be Miredo itself on Linux/FreeBSD/OpenBSD/NetBSD.