In an attempt to encourage developers to sell their apps through the Amazon Appstore, Amazon has announced a new virtual currency for buying Kindle Fire games or apps and making in-app purchases.

From May 2013, and initially only in the US, Amazon Appstore customers will have an alternative way to pay for purchases, including in-app items, for apps on Kindle Fire.

Amazon Appstore debuted in March 2011 with 4,000 apps. Kindle Fire was launched six month later and grabbed a substantial share of the tablet market, particularly in the US. Indeed, some figures, see Kindle Fire Top Android Tablet, suggest it has 33% of the global Android tablet market share, accounting for around 55% of  Android tablets in the US.

Amazon Appstore, however, hasn't been as successful in attracting apps. It currently has more than 68,000 apps - by comparison Google and Apple each have more than 700,000.

Developers will continue to get 70% revenue share, paid in dollars, so the success of the scheme will be down to how consumers react. To get the ball rolling Amazon is planning to give out "tens of millions of dollars worth of Coins" to customers to spend on Kindle Fire apps, games, or in-app items. Subscriptions are excluded from the scheme.

One attraction of virtual currency is that while you have some it encourages you to spend. Each Amazon coin is worth one cent so they are particularly suitable for small in-app purchases. But, as developers are finding out, in-app revenue, even from very small sum, can mount up.