4chan is an English-language imageboard website. Users generally post anonymously, with the most recent posts appearing above the rest. 4chan is split into various boards with their own specific content and guidelines. Registration is not required, nor is it possible (except for staff).
Tumblr (stylized in its logo as tumblr.) is a microblogging platform and social networking website founded by David Karp and owned by Yahoo! Inc. The service allows users to post multimedia and other content to a short-form blog. Users can follow other users' blogs, as well as make their blogs private. Much of the website's features are accessed from the "dashboard" interface, where the option to post content and posts of followed blogs appear.