This article will focus primarily on the first type: the easiest-to-use, downloadable simulators that are safe to run on modern hardware and mobile devices.
Inside, the desktop was a museum of choices. Sidebar widgets, proud and slightly smug, displayed weather and a slideshow of photos you had never taken. The sidebar’s translucent panels cast faint shadows on the wallpaper: rolling hills that could have been the green of a million default desktops. Every window opened with a theatrical cascade, a little flourish of shadow and bevel, as if the interface were apologizing for existing yet determined to delight.
Because this is a simulator and not a full OS, the "installation" is either instant (web) or a simple file extraction.