The top-right corner of the browser holds a few additional controls: a clock, a power-management / battery indicator, a network status indicator, and a drop-down menu that's the same as the "wrench" icon in Chrome. From there you can access many of the same settings you'd expect to find in Chrome as well, although they are far from the full range of options available in the system. For that, you'll need to really dig under the hood.
The command-line console is where Chromium OS's Linux underpinnings become clear. Press Ctrl-Alt-T and you'll be greeted with a text-only command line, into which you can type any number of common Linux commands.
Note that a lot of things have been stripped down or tossed out entirely, so some commands might not work as expected, or at all. In some ways the Linux substrate for Chromium OS is akin to the mini-Linux plus BusyBox found in hardware devices like routers: there's only what's needed to run the system and no more than that.
Most every command must be run with administrator or root privileges to be effective. You'll need to use the Linux sudo command to make this happen. You'll also need the admin password to run sudo, which might vary from build to build. In the Geeklad VirtualBox build, the admin password is just password; in many other builds, the admin password is chromos.
The changes that can be made under the hood right now depend entirely on how much spelunking you're willing to perform. On some builds, it's possible to use the xrandr command to change the display size -- handy if Chromium OS is stuck at a resolution you know is a good deal smaller than what your display hardware is capable of. Many things, however, are manifestly not possible right now: adding packages to a running system, for instance. At this stage it only seems possible to do that by adding said packages to the system-image build process.
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