One of the new, fast-growing categories of entrepreneurs – thanks to the present times of ever-increasing popularity of smartphones - is apparently the category of the “the app developers;” those who are engaged in creating programs for the countless mobile handsets.

The ‘applications’ industry, which has largely grown up around the Apple iPhone – with over 140,000 iPhone applications been developed since Apple’s July 2008 opening of the Apps Store to third-party developers -, has recently been invaded by a number of other companies – including Research in Motion, Nokia, Samsung, Microsoft, and Google.

Going by the statistics revealed by advertising firm AdMob, despite the fact that applications cost only a few dollars for download, and most of them are even ‘free’, the app market has been valued at almost two and a half billion dollars per year.

With the unprecedented and unthought-of of popularity of apps, a gold rush mentality is fast raising its head among the newest breed of entrepreneurs – the independent software developers, some of whom have already hit the millions.

One such entrepreneur ‘developer’, the San Francisco-based Dave Castelnuovo, admits that the success of his app has totally taken him by surprise. Castelnuovo, the co-creator of the $99-priced iPhone game ‘Pocket God’, is totally bewildered at the over two million downloads of the app; and modestly admits: “We are currently the best-selling app of all time.”