Twitter founders Evan Williams and Biz Stone are set to launch two new social networking sites that they hope will spring an “evolutionary leap” in online sharing.

These new sites – Medium and Branch – have been created to address specific needs that users have. They are both publishing platforms that will be used to share articles, pictures and text.

“Our philosophy is that quality begets quality, so we will grow Medium smartly, ensuring that our platform is valuable to everyone in this increasingly mobile, connected, and noisy world,” Williams told the Guardian. Medium is based around themed photo and writing collections.

The other new venture is Branch, a site that will allow users to continue and expand their conversations and dialogue without being confined to the 140 character limit. It is described as a site that will “combine the intimacy of a dinner table conversation with the power of the internet.” Josh Miller, the head of product at Branch, says, “Between articles, blog posts and tweets, the internet is dominated by monologues. So we want to build a home for dialogues online.”

The second acts of social network founders tend to attract attention – and can come up short in comparison with original successes.

Some do well, such as Square, Inc. Square was developed by the co-founder and executive chairman of Twitter, Jack Dorsey, and is a small business platform to accept debit and credit cards on a mobile device. This was a successful new scheme and more than 1 million people now use Square to process credit cards. Another victorious website was FriendFeed, created by Paul Buchheit, the founder of Gmail. FriendFeed was launched in 2007 and then acquired by Facebook in 2009.

But not all new ventures have been a big hit. Take Wirehog for example; created by the founders of Facebook (Andrew McCollum, Mark Zuckerberg, Adam D’Angelo and Sean Parker), it was a program that allowed people to share files directly between computers. It was launched in October, 2004, but lasted less than two years before it was taken down and killed, so that the company could focus completely on Facebook.

Evan Williams and Biz Stone believe both Medium and Branch will climb the social networking ladder and become big hit projects. The success of these sites will be judged on the conversation quality and return rate of its users, rather than the number of sign ups. With Medium allowing people to choose the level of contribution they prefer and Branch bringing the simplicity of Twitter, this could well bring the leap in online sharing that Williams and Stone are hoping for.