Software developers for Windows and Mac computers will be able to get their hands on a software developer's kit (SDK) that will put Skype's VoIP calling features into almost any app.

On Wednesday, Skype is offering a limited, invite-only beta release of the SDK, called SkypeKit, to those who request it. SkypeKit beta will work for Windows (x86) and Mac OS X.

The well-known VoIP company first announced SkypeKit in late June, and released its first beta of the program for Linux developers.

Adding Skype modules, like free VoIP calling and video chat to apps, is a big win for Skype's business model, but can also benefit users by letting them use Skype functionality alongside a program's other features without having to fire up a separate Skype app.

It will be interesting to see where these Skype "plug-ins" will pop up.

Jessica Dolcourt reviews smartphones and cell phones, covers handset news, and pens the monthly column Smartphones Unlocked. A senior editor, she started at CNET in 2006 and spent four years reviewing mobile and desktop software before taking on devices.