Keynote’s .key files are a very popular presentation format used by Mac users, however sometimes we require to open Keynotes in Microsoft PowerPoint. powerpoint is historically available on Windows but also in Mac with the powerpoint 2011 for Mac version.
Keynote is only available on OS X and there is no native version of Keynote on Windows, however if you have Keynote in your Mac you can then export your .key files to .ppt presentations compatible with Microsoft powerpoint. However, the exported presentation may not keep all the original transitions and animations available on Keynote so this procedure is better to export simple presentations.
powerpoint can’t open Keynote .ppt files by itself, but using other other online tools like Zamzar then it is possible to convert Keynote to powerpoint, as detailed in their article supporting Keynote conversion to powerpoint presentations. Besides powerpoint, Zamzar allows to convert .key files to other formats like .html, .tif, .png, .pdf, .mov, etc.