What CP/NC is

CP/NC is mostly compatible to CP/M 2.2, with some inspiration from 3.0. It offers:

A CP/M-compatible file system
BDOS-level (and some BIOS-level) compatibility to CP/M; many CP/M programs will just run
CCP-level compatibility to CP/M
Up to four virtual 256KB disks on a PCMCIA SRAM card
A VT52-compatible console screen (although with only 8 lines)
Common CP/M commands (PIP, STAT, DUMP, SYSGEN, etc)
A serial console via IOBYTE (try STAT CON:=TTY:)
more than 48K bytes of transient memory

What CP/NC is Not

These are also some differences between CP/NC and CP/M. For further details, see the file docs/system.txt in the distribution archive.

There are currently no file attributes, so files cannot be marked hidden or read-only.
There is an AUX: device instead of PUN: and RDR:.
There is an IOBYTE, but BDOS functions 7 and 8 query the AUX: status, like in CP/M 3.0.
Some CP/M 2.2 BDOS routines are not implemented: Get Allocation Vector (1Bh), Write Protect Disk (1Ch), Get R/O Vector (1Dh), Set Attributes (1Eh), Get DPA (1Fh), and Write Random with Zero Fill (28h).
There are a few CP/M 3.0 BDOS routines and a few CP/NC-specific routines.
The BIOS disk routines are unimplemented; programs that call them will abort.
The BIOS, BDOS, and CCP currently form one single blob, so the CCP does not reside in transient memory.
Not all control keys are supported (^C,^H,^S,^Q,^X, and DEL do work).