7PLUS is an encoder vaguely similar to Unix's UUENCODE.

It uses a very effective radix216 encoding and incorporates diverse
mechanisms to ensure decoded data is not corrupted.  It also includes an
interactive repair mechanism which allows the repair of damaged files
using correction files, thus eliminating the need to retransmit entire
files. In case of a corruption, only the faulty sections are resent.

7PLUS is only meant to be used within the Packet Radio network for the
tranport of binary data through Packet Radio mail.  It cannot be used
for Internet eMail since it needs a (almost) transparent path from end
to end.