Less than six months after rolling out the Twitter application TweepML, Seattle entrepreneur and developer Marcelo Calbucci has put the service up for sale on the public auction site Flippa. Calbucci set a "Buy it Now" price of $79,000, which he told us is "somewhat arbitrary" but does value the service at what he called the bargain price of less than $1 per unique visitor per month. He said he'd be happy with an offer over $10,000.

Started as a side project by the Seattle 2.0 and Sampa founder, TweepML was unveiled just a few months before Twitter itself introduced its list functionality. While the two services often drew comparisons, Calbucci said he was surprised that TweepML continued to attract users despite the new competition.

"Contrary to what we thought, people continued to use the service and find it valuable," he said. "Between the many reasons, TweepML has a simpler and faster interface to create larger lists of Twitter users, but also TweepML allows you to follow directly members of a list, all of them or just some of them. The service today allows you even to take a Twitter List and follow just the individuals you want to follow."

So why sell now? Calbucci answers that question on the auction site, saying he just doesn't have time to manage it. He writes:

"The first question people would probably ask me is why am I selling it and what's the catch. The answer is simple: I need to focus on fewer projects on my life. TweepML was a great project and got instantaneous traction. But over the months I've been busy doing other things and not giving it the attention it needs to continue to grow and flourish either as a service or as a complement to another service. The key to successful building a business is focus, and I'm doing too many things at once and that's not working. So, I'm selling TweepML so someone else can give it the deserved attention."

TweepML claimed an average of 100,000 unique visitors and 450,000 page views per month, though January traffic stood at 79,000 unique visitors and 228,000 page views. It lists advertising revenue of $200 per month. The sale includes all domains (including TweepML.org and TwitterList.com), code and the @tweepml Twitter account, which now stands at more than 32,000 followers. To date, Calbucci notes that 9,500 lists have been created with TweepML.

Bidding for the assets starts at $1,000, with the auction set to conclude in 17 days.