5 is a portable and extensible stack-oriented array language that combines the features of APL and Forth and some ideas from Perl to yield a highly interactive environment for the professional developer as well as students of computer science. The interpreter is very lightweight (about 650 Kb all in all, including documentation) and runs readily on a variety of operating systems including Windows, LINUX, Mac OS X and even OpenVMS (VAX, Alpha, Itanium). 5 is Open Source and resides on SourceForge[1].