ZSCII is the character encoding used in Infocom games, in conjunction with the Z-code game file format.
It is based on ASCII, using the normal printable characters and some of the control characters in their standard ASCII code positions, supplemented with some additional characters and control functions (e.g., representations of cursor movement and function keys). Some of these code positions are defined only for input, some only for output, and some for both. Code positions up to 1023 could be used in this system, but only the positions up to 254 are actually defined, making it suitable for an 8-bit encoding. However, the actual encoding is a somewhat complicated system of variable bit-group lengths (including 5-bit words) for the dual purposes of compactness and obscurity (making it so that a raw file dump doesn't immediately reveal any ASCII-like strings).