(Named after TI-85 processor, Zilog Z80. Not to be confused with zsh, <flamebait>a shell not quite as good as bash</flamebait>)
A shell for running machine code in TI-85 graphing calculator.
It was first released in 1994, and was the first machine code shell for TI-85. The installation method was simple: The shell came as a backup file that was transferred from computer to calculator. There was some interesting "backdoor" in backup files that let the clever people to assign arbitrary targets for CUSTOM menu buttons (that were usually used for storing shortcuts to often-used commands). After installation, the ZShell could be started with CUSTOM, F1.
The actual programs were then given as string files (.85S) that contained the binaries.
ZShell was revolutionary: Of course, TI-85 BASIC programs were slow, slow, and slow; machine code, then, was blindingly fast. Many other shells later appeared, blurring the boundary between imagination and reality.
The latest (and last) version of ZShell is 4.0, written by Magnus Hagander.