Chromium OS vs Plan 9

Since you only have the browser, you cannot install applications (outside Chrome Apps which are decently protected by their limited API and the Chrome Web Store). This means no harmful virus, and also nearly no way you can screw your system. Everything will just work.

Chromium's system UI uses as little screen space as possible by combining apps and standard web pages into a minimal tab strip: While existing operating systems have web tabs and native applications in two separate strips, Chromium OS combines these, giving access to everything from one strip. The tab is the equivalent of a desktop application's title bar; the frame containing the tabs is a simple mechanism for managing sets of those applications and pages.

Because Chromium OS is designed for users who spend most of their computer time on the Web, it is intended for use in computers with little local storage and fast boot-up times.

Plan 9's design is very orthogonal and well done.

With Plan 9, computers are turned into terminals where you can access files and processing units which can be located elsewhere. Data storage is handled by another external server. This means that instead of each person having their own individual computer with all the required parts, all of the computing and storage is done in a central area and everything is networked in together.