Jamatto provides a way to give readers the opportunity to make a one-time micro-donation for articles that they like.
One can also set it up as a way to sell articles or subscriptions.
What is the smallest amount that can be processed?
$.01?
Or even $.001? (A mill, a legal unit of U.S.currency)
I think you'd have to ask the Jamatto people to get a definitive answer, but just fiddling with an HTML page on my local disk I was able to get the donate button to show a donation amount as low as 0.1¢, that is, $0.001.