An early series of UNIX workstations from Sun Microsystems, all based around the Motorola 68010 processor. Unlike the later m68k processors, the 68010 was not capable of addressing 32 bits of RAM. As a result, even though most of the Sun2 machines could hold 12mb of RAM, they could only use 10mb or so (Sadly, I've forgotten the precise limit)
While little information about the Sun2 arch is still available, it's unfair that they're forgotten. The Sun 1 and Sun 100U were a groundbreaking concept in the making, but the Sun2 series, especially the 2/50 and 2/120, was the first workstation line to be produced in quantity, introduced in 1982.
The best-known Sun-2 is, of course, the venerable Sun 2/120, the closest to usable as a standalone system, the ultra-low-budget option for UNIX enthusiasts in the mid to late 80's. It ran vi and it had a reasonable amount of protected memory, a leg up on 286-based XENIX systems. Under SunOS 3.x, it wasn't half-bad. Some of the Sun2 machines were capable of running SunOS 4.x, even if it was unbelievably slow.
Sadly, by the quality control standards of the late eighties, the 2/120 was a horrible bucket of shit. Terminally flaky serial chipsets and memory boards, passive backplanes, limited expandability and badly designed chassis made them a masochist's dream.
Surprisingly enough, there's a handful of Sun2's still extant, at least enough for one brave soul to justify the NetBSD/Sun2 port to himself.