A2Central has published an article about their impressions of some new products from UltimateApple2 and ReactiveMicro, an NSC successor that is slimmer than the original No-Slot Clock and features a user replaceable coin cell battery.
About the original NSC, it was explained that “…No Apple II (prior to the IIGS) had a built-in clock. (…) All alternatives at the time were boards installed in one of the expansion slots (…) You could install the NSC into just about any other 28-pin ROM socket, piggyback the ROM into the NSC, patch your ProDOS and viola’ — your Apple II could tell the time…”
The new and improved NSC is still being developed, and there is no price defined yet.
Link: A2Central