Plugin/Widget for browser dependent downloads

I am looking for a plugin where I can offer a (download) link depending on which operating system the user agent is running on.

E.g. if the user is using windows I want the download link to point to my windows version of my software, if the user uses a mac I want to offer that download.

Of course it should also be possible to display different text for both versions…

I searched the plugins but did not find any matching. Is there something out like that?