This is part of a series of posts this week on happenings in the sprawling but always succinct world of Twitter.

Twitter can be used to network, make friends or keep up with Britney Spears. And soon it will become a way to transfer money over the Web.

Twitpay is a start-up that aims to allow people to send small payments through Twitter. To do this they include the recipients’ username in their message. For example, posting the update “@johnsmith twitpay $10 for lunch” would deliver the cash to that Twitterer’s Twitpay account. The company monitors the public stream of messages for the keyword “twitpay” and facilitates the exchange. You replenish your Twitpay account using a site like PayPal. Once recipients have accumulated more than $10 in their accounts, the balance can be cashed out in the form of an Amazon gift card. For all transfers exceeding $1, Twitpay will take a flat cut of 5 cents.

In its simplest form, the service is a quick way to settle a lunch tab or pick up a round of drinks on a friend’s birthday. But Michael D. Ivey, its chief executive and co-founder, says it could also make it easier to donate money during a disaster like Hurricane Katrina or an earthquake. “Ideally we want to enable social giving on Twitter,” he said. “But beyond that, we could enable charitable giving, such as to the Red Cross. We’re very excited to be able to help people do good over Twitter.”

Along with many of the third-party applications that make use of Twitter’s platform, Twitpay has no official ties to Twitter, which allows people to post messages up to 140 characters in length. But along with the Shorty Awards, Mr. Tweet and the multitude of other sites and third-party applications springing up around the platform, Twitpay is another example of the way Twitter is forming an ecosystem of its own.

The service is still in a trial phase, but Mr. Ivey said the company was actively working to obtain financing and is in discussions with several groups.