Facebook is finally launching an App Store of its own. The store is currently in beta testing, but the idea is for something similar to the Apple or Google app stores. It will provide a place to promote and discover new social apps and is due to go live in the coming weeks.

Significantly as well as helping us all find new Facebook apps it will also allow developers to charge users for downloading apps for the first time.

This will not only boost revenues for developers (previously in-app purchases were available), but crucially it will create a new income stream for Facebook.

The move will be welcomed by investors as Facebook this week lays out its plans for its initial public offering.

The launch of the Facebook App Store will likely provide a major boost to the number of apps being downloaded, paid or free, as it becomes easier to find new apps be they for the web, iOS or Android platforms.

It will also fill in another slide in the ‘how Facebook makes money out of mobile’ presentation’. It is a key area investors and Facebook watchers have been asking questions about and an area where Facebook has yet to provide many answers.

The Facebook App Store will allow users to search for apps by category and ratings as well as those being promoted by Facebook.

As well as a list of top apps the Facebook App Store will have a neat social function. It will recommend apps to users based on what their friends are using — they can app sync if you like. You can see what they have cooking here.

The launch comes as Facebook updates its IPO filing again with a warning to investors that product development comes before revenue:

“Our culture also prioritizes our user engagement over short-term financial results, and we frequently make product decisions that may reduce our short-term revenue or profitability if we believe that the decisions are consistent with our mission and benefit the aggregate user experience and will thereby improve our financial performance over the long term. As an example, we believe that the recent trend of our DAUs increasing more rapidly than the increase in the number of ads delivered has been due in part to certain pages having fewer ads per page as a result of these kinds of product decisions.”