Hikvision

Hikvision Camera developers page
The Hikvision DS-2CD2032-I and DS-2CD2432F-IW cameras use Linux and BusyBox. As of May 2014 the versions are:

Linux version 2.6.38.8 (wangqian@ipcteam2) (gcc version 4.6.1 (Sourcery CodeBench Lite 2011.09-70) ) #18 PREEMPT Wed Jan 8 14:47:56 CST 2014

BusyBox v1.19.3 (2013-11-01 10:10:26 CST) built-in shell (ash)

The main chip is labelled Ambarella A5s-CO-RH which is system-on-a-chip that integrates an ARM1136J-S CPU,
 * a other subsystem: Ambarella A5s.

The CPU uses the ARMv6 instruction set with media extensions: ARM1136
 * 256MB DDR3 SDRAM

Useful links:
mroek's teardown and pictures of the Hikvision DS-2CD2032-I hardware. http://www.cctvforum.com/viewtopic.php?f=19&t=37006

Ambarella A5s http://www.ambarella.com/uploads/docs/A5s%20IP%20Cam%20Brief%20121013.pdf

BusyBox combines tiny versions of many common UNIX utilities into a single small executable. Open source, free. http://www.busybox.net/

GCC, the GNU Compiler Collection https://gcc.gnu.org/

Sourcery CodeBench is a complete development environment for embedded C/C++ development on many architectures. $100 to $3000 https://store1.mentor.com

CBX notes on his many development endeavors http://www.cctvforum.com/viewtopic.php?t=39874