The idea had already been initiated in 2007, but the first release was in 2010 due to typical geeky laziness.
Flattr was founded to help people share money, not just content. Before Flattr, the only reasonable way to donate has been to use Paypal or other systems to send money to people. The threshold for this is quite high. People would just ignore the option to send donations if it wasn’t for a really important cause. Sending just a small sum has always been a pain in the ass. Who would ever even login to a payment system just to donate €0.01? And €10 was just too high for just one blog entry we liked…
Flattr solves this issue. When you’re registered to flattr, you pay a small monthly fee. You set the amount yourself. At the end of the month, that fee is divided between all the things you flattered. You’re always logged in to the account. That means that giving someone some flattr-love is just a button away. And you should! Clicking one more button doesn’t add to your fee, it just divides the fee between more people! Flattr tries to encourage people to share. Not only pieces of content, but also some money to support the people who created them. With love!
Flattr has no different user types. We know that everybody that create also uses other content. And vice versa. We make no difference between people.
Flattr can be used as a complement to accepting donations. Or to having advertising on your blog. Or to help getting small donations you never get for your open source software.