One of the ways 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. 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 you enjoy.
Flattr is aimed at solving this problem. 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.
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.