Twitter cofounder Evan Williams took less than 140 characters to ask on Monday: “What are the limitations of an invite-only conversation? What do you gain and what do you lose?”

The question was followed by a link to a discussion on Branch, a new site that he helped launch in public beta this week that enables this kind of conversation.

Billing itself as a “new way to talk to each other,” Branch is a startup launched through Obvious Corp., an incubator started by Williams and fellow Twitter cofounder Biz Stone. Paired with a second Obvious Corp. launch this week, Medium, a publishing tool “built from scratch,” it’s clear the two Web entrepreneurs believe there is still wide room for innovation in online discourse.

Before creating a new style of conversing with Twitter, Stone and Williams started Blogger, one of the first blog-publishing services, in 1999. “For the people that helped invent the medium, to be revisiting it is exciting,” says Anil Dash, a longtime technology blogger and entrepreneur who was also an informal advisor to Branch. 

Branch hovers in a space somewhere between a private, lengthy e-mail thread or online forum and a pithy, public stream of tweets. Discussions appear in chains, but posts can be only up to 750 characters, and anyone can view them. Unlike Twitter, not everyone can actually participate in a conversation; instead, a current participant must grant access. In addition, tangential topics can be “branched” from the main discourse, and new topics can be imported from Twitter itself. One can imagine a heated or thoughtful Twitter exchange ending with a “let’s take this over to Branch.” As one of the site’s founders, Josh Miller, notes, there are discussions that warrant more than 140 characters.

With few substantial changes in Web publishing or commenting methods over the last decade, the time may be right for both of these products, Dash says.

In his view, Branch, which has now raised $2 million in venture funding, would be successful “if people saw what those of us at the dawn of blogs saw—that you can have wonderful, meaningful conversations online. It’s not just people tearing each other down.”

The other Obvious Corp. venture, Medium, offers new ways to organize photos and text publishing with the goal of improving quality and participation rather than offering yet another way to share.

Branch’s future may be hinted at on the site Quora, which similarly enables people to engage in discussions and has already raised $61 million in venture funds since it launched in 2010. Quora is different, though, in that anyone can contribute and the focus is on answering topical questions, rather than conversing.

On Quora, Branch cofounder Miller asked the Quora founders whether they believe Branch is the competition (they have yet to answer). Miller also recently started tracking answers to the discussion: “What is it like to be acquired by Facebook?”