moneyOnline forums and communities present a largely untapped opportunity for making money — at least according to Dan Gill, cofounder and chief executive of Huddler.

The San Francisco startup is officially launching today. It’s one of those weird launches where the company has actually been working with customers for more than a year, and is only now getting around to telling the media that it exists. Gill said he wanted to make sure the technology was solid before doing too much to publicize it and attract competition.

Community-building software is a broad category, but Huddler approaches the market with a specific audience and mission. It’s looking for popular, product-focused forums that are built on either vBulletin or phpBB technology. Huddler contacts the owner of the site, offering to modernize the forum and bring in more money too.

Gill gave me a long list of benefits that Huddler can offer over older platforms. It gives the sites a makeover, so they look a bit less old-fashioned, not to mention more advertising-friendly. It optimizes the pages for search engines, and also makes them easier to share through Facebook Connect. And all the software is hosted online, rather than installed on someone’s computer, which means there’s less hassle for whoever’s managing the site.

Financially, there’s not much risk to the forum owner, since the software is free. Huddler is only paid by through a percentage of the increased revenue that it brings to a site. That revenue boost comes in a number of ways, Gill said — since the sites are product-focused, Huddler creates a product page with a link where visitors can buy the item in question. It also allows companies selling related products to create their own pages on the forum and engage with the community. And of course the sites can run advertising.

The transition to Huddler can be a challenging one because of the technology issues, as well as the likelihood that change will upset some forum members. Gill didn’t offer any details, but he hinted that he has seen his share of angry comments from users who didn’t like a new forum. But Huddler has become more proficient at both moving content to a new site and preparing users for the change, he said.

There are now 24 sites using Huddler, adding up to a total of 9 million unique monthly visitors. The success stories include EpicSki, which saw a 70 percent increase in natural search traffic after switching to Huddler, and DenimBlog, which doubled pageviews in two months and is now bringing in three times the amount of revenue.

Huddler raised $5.5 million in funding from New Enterprise Associates last year. For now, the company is focusing on existing forums because they’ve already got the audience, but Gill said, “There’s no reason you won’t be able to start your own Huddles in the future.”

[image via Flickr/Daniel Borman]