Posterous was a blogging platform, which has become yet another of the Web-based services that got bought out by another company (Twitter in this case) and eventually terminated its service, dumping user data if it isn't preserved somewhere else, and giving an effusive press release about how it's all for the greater good of the Internet public and the buzzword-laden business models of Internet companies. (These shutdowns are not always April Fool jokes.)
A means of data export was provided for users, who had through April 30, 2013 to get their data before it went away. This was provided in the form of a ZIP file containing the HTML, images, and other files in hosted sites; some other providers have provided import procedures for the format used. There is also an Archive Team project attempting to grab as much as it can of publicly-accessible sites on that service, as they have done for other now-defunct services like GeoCities. They did very well at getting publicly-accessible Posterous data, despite that site imposing (for a while) automated bans of people who try such bulk downloads.