“Binning” when you combine the signal from adjacent pixels in a camera which reduces the resolution and improves the signal quality.
All CMOS cameras use software binning. They can’t do “hardware” binning in the same way a CCD camera can – by adding the electrical charges on a pixel up, before analogue-to-digital-conversion.
Altair GPCAM, Hypercam CMOS cameras use averaging when binning, rather than adding the binned pixel values like a CCD.
CMOS-style binning reduces the noise level with averaging rather than increasing relative pixel brightness like addition does (both techniques give the same increase in signal-to-noise ratio, which is the real goal).
Some might say additive pixel brightness increase is an important feature of CCD binning. Brightness however is not that important in itself, because it’s really just a number (a value per pixel) and it can be fixed post-processing during stretching of the image, or increased proportionally until a dim image feature appears.
The fact that CMOS cameras use “averaging” means that it’s often a good idea to turn up the gain more when you use binning to brighten the image. Since the noise has already been reduced by binning, it will be easier to process the image than if you turn up the gain the same amount without binning.