UTF-7 is/was mostly for email, which is not an 8-bit clean transport. It is obsolete and can't encode supplemental planes (except via surrogate pairs, which were meant for UTF-16).

There is also UTF-9, from an April Fools RFC, meant for use on hosts with 36-bit words such as the PDP-10.

I meant to specify, the aim of UTF-7 is better performed by using UTF-8 with `Content-Transfer-Encoding: quoted-printable`