Interesting desktop environments (or complex UIs) that I would like to have a closer look at:

• NLS -(Engelbart)
• Sketchpad (Sutherland)
• Xerox Star
• Arcan - see also HN discussion
• TempleOS - from-scratch-OS
• DexUI - futuristic Linux desktop
• Plan 9
• Plan B (Ballesteros)

Facets to investigate:

• architecture
• multi-display/computer capabilities
• automation / user scripting
• compatibility with existing/other systems
• basic UI paradigms
• inspirations from other UIs
• efficiency with regard to typical tasks (file copying, text manipulation) (we need a corpus of typical tasks)
• persistence of sessions / applications