Substack, an online publishing platform, has acquired Letter, an Australian public correspondence startup facilitating written debate, to help foster the community and more engagement between Substack writers and possibly between writers and readers.

The financial terms of the deal were not disclosed; however, the co-founders of Letter, Dayne and Clyde Rathbone, and their team will be joining Substack. The team will relocate from Australia to San Francisco to develop the infrastructure and support independent writers require.

Letter is a startup offering a free-to-use, ad-free platform for written qualitative debates, aiming to encourage thoughtful discussions. The platform has attracted historians, philosophers, and political activists, such as Noam Chomsky, Yuval Noah Harari, and Ayaan Hirsi Ali. Letter has not previously raised any venture capital apart from a small round of angel investment.   

Founded in 2017, Substack offers a publishing platform encompassing design, analytics, and payment infrastructure to assist newsletter subscriptions. The platform enables writers to focus on content creation and monetization via subscriptions. Substack’s top 10 publishers have been reported to bring in more than USD 20 million a year in combined subscription revenue.