It's less than a year since Apple went open source and there are already 100,000 applications and counting but which ones are any good and which are really awful; Forbes.com have taken a look at what makes a successful app and somewhat unsurprisingly, it's how genuinely useful they are.

One of the app success stories of the year was created by Danika Landers, a 29-year-old Web designer. She walked into a public toilet and was so disgusted by the appalling conditions that she decided to create a web site fully dedicated to helping people find clean bathrooms: SitOrSquat.

SitOrSquat, which features user-generated recommendations of the best public toilets in the US, was such a hit that Procter & Gamble, maker of Charmin, signed the toilet paperbrand as a sponsor. It then rolled out a new SitOrSquat mobile application this year. With 400,000 downloads, the free app has become one of the most talked about among consumers and companies,  and is one of Forbes CMO Network's top 10 branded mobile applications of 2009. 

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