Plan 9 from Bell Labs

This Unix OS from Bell Labs works on nearly all home computer architectures, and is a lightweight solution for older computers. The operating system only takes up ~100MB of your hard drive. It features a GUI interface called rio directly on top of the Unix's system. Other software applications include a text editor (acme or Sam), a mail client(mail and upas), and a suite of compilers. It is a very simple operating system for Unix programmers and lovers.





http://plan9.bell-labs.com/plan9/license.html
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