The SLC-1 clock/calendar is a pretty nice hack, installed "in series" with the console serial terminal, it remains utterly passive until it detects text strings you specify, at which time it can output other text strings. The idea is, at boot time your startup script can maneuver the SLC-1 to issue a "set time and date" command instead of having to set it manually every time you boot (like the original IBM PC and variants.)

FILENAME? 

MAPPED NOVA 3 RDOS REV 6.60
DATE (M/D/Y) ? 3 3 2005
TIME (H:M:S) ? 16 5

Whenever it sees "DATE (M/D/Y)" it outputs the date in the right format. Very fancy!

It's a little computer built around a 6502, a few K of RAM and ROM, and a battery-backed up quartz crystal clock, and a nice LED display for MM DD HH MM SS. A couple of front panel switches determine it's mode, ONLINE/OFFLINE, that sort of thing. The internal structure is primitive, but pleasantly so. In addition to obvious commands for setting time and pattern texts, there's basically what we'd generally call a debugger, with which you poke raw hex values into memory ("text delimter is stored in address 0x53be" type thing).

When I got it it was inoperable; the fan was frozen, and all the TTL junk inside makes a lot of heat! -- PC board coatings turned brown, and a power supply cap went open, making 5VDC into a lumpy 6V squarewave (more or less). Cooling was utterly inadequate anyways; the case being more or less ruined already (big chunk taken out of the back, covered in cracks, warped from the heat) I cut a bunch of holes in the bottom and top, and now the new fan actually moves air through the cabinet instead of basically circulating the hot air evenly.