The first new venture is Medium, a Pinterest competitor that enables users to share images, quotes and other data in public collections.
"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," The Guardian quotes Williams as saying.
Williams and Stone have also unveiled Branch, a place where Twitter users can continue their conversations without the restrictions of the 140 character limit.
"Between articles, blog posts and tweets, the internet is dominated by monologues. So we want to build a home for dialogues online, by combining the intimacy of a dinner table conversation with the power of the internet," said Branch head of product Josh Miller.
Twitter users can sign into the new services with their accounts for a preview of what they will offer, but full use is restricted to invite-only beta.