trivial-gray-streams is a trivial library which provides an extremely
thin compatibility layer for Gray streams.

From David N. Gray's STREAM-DEFINITION-BY-USER proposal:

"Common Lisp does not provide a standard way for users to define
their own streams for use by the standard I/O functions. This impedes
the development of window systems for Common Lisp because, while
there are standard Common Lisp I/O functions and there are beginning
to be standard window systems, there is no portable way to connect
them together to make a portable Common Lisp window system.  There
are also many applications where users might want to define their
own filter streams for doing things like printer device control,
report formatting, character code translation, or encryption/decryption."

WWW: http://www.cliki.net/trivial-gray-streams