I was just wondering if anyone could provide names and a bit of background on the Operating Systems the current day DSLRs (namely, Nikon, Canon) use.
So far what we know based on ML work
DRYOS version 2.3, release #0023
DRYOS version 2.3, release #0039
DRYOS version 2.3, release #0043
DRYOS version 2.3, release #0044 or #0049
DRYOS version 2.3, release #0047
I'm generalizing but I see in Canon P&S they tend to reuse DIGIC processors so a quick check on a Wiki indicated that DRYOS is used.
It isn't specifically mentioned but ML developers indicate that they think this DRYOS is a derivative of uLTRON. They also did indicate that some concepts in DRYOS could be compared to or understood from VxWorks.
BusyBox 1.4.2 (Linux Kernel)
BusyBox 1.13.4 (Linux Kernel)
In the case of Canon and Nikon the current models are all proprietary.
There are apps for Android devices that allow them to control a Canon camera via a USB cable, but the camera is not running the Android OS.
Of course in certain areas the firmware includes compatibility with accepted standards such as USB, DPOF, EXIF, JPEG, etc.
In the past some of the early Canon DIGIC boards ran Datalite ROM-DOS on an x86 compatable NEC V20 emulator. Beginning with DIGIC II the processor was embedded in proprietary ASICs and ran on the VxWorks OS. This continued with the DIGIC III line of cameras. DIGIC 4 and later cameras have run on Canon's proprietary DRYOS, the kernal of which is built around µlTRON4.0
In the case of most recent Canon DSLRs that have video recording capability, a third party firmware add-on named Magic Lantern is available. It does not replace the original firmware but runs within it. There are similar firmware add-ons for some Nikon DSLRs, but none have been developed to the point they are consistently stable as of early 2013.
There are a few cameras runnin Android. The Nikon Coolpix S800c for example. There will probably be more to come. As you guessed, most of the current DSLRs run on proprietary operating systems, although there is the CHDK (Canon Hack Development Kit) and Magic Lantern firmware hacks for Canon, that provide some extra functionality to the OS.
There was also a similar Nikon project, but I don't think it ever got to the stage where it was usable.