einstein's legacy (http://www.einsteinslegacy.com) has announced Monochrome 2.2.1 for OS X. It's an upgrade of the application for converting batches of color images to grayscale.

Monochrome gives you control over the conversion process and applied effects, so you can create a consistent-looking set of output images. The 2.2.1 update expands the available GPU-based image rendering effects and adds new options for slide show playback.previewing, printing and sharing images.

Monochrome is available for US$19.99 from the Mac App Store in the Photography category. It requires Mac OS X 10.9 or higher.