Gazelle is a research web browser which Microsoft Research announced in early 2009. The central notion of the project is to apply operating system principles to browser construction. In particular, the browser has a secure kernel, modeled after an operating system kernel, and various web sources run as separate "principals" above that, similar to user-space processes in an operating system. The goal of doing this is to prevent bad code from one web source to affect the rendering or processing of code from other web sources. Browser plugins are also managed as principals.
By the July 2009 announcement of Google Chrome OS, Gazelle was seen as a possible alternative Microsoft architectural approach compared to Google's direction. That is, rather than the operating system being reduced in role to that of a browser, the browser would be strengthened using operating system principles.
ServiceOS is also related to the browser architectures.