Prime Indicator is an AppIndicator for laptops with Nvidia Optimus, allowing users to quickly switch between Intel and Nvidia graphics.

The original Prime Indicator hasn't been updated since February, 2015. André Brait forked the indicator (while also using code from the Linux Mint version), improving it with both new functionality and bug fixes, and the new app is called Prime Indicator Plus.

Update: Prime Indicator was abandoned, but it was later forked, and it now includes quite a few new features. The Ubuntu PPA installation instructions in this article now install the fork (called Prime Indicator Plus). For more about Prime Indicator Plus, see this article:

As you probably know, the Nvidia graphics drivers have received initial Optimus support a while back. Currently, the Nvidia GPU can be used to render the desktop, but there's no power saving yet. That means you can for instance play games or watch videos using hardware acceleration.

But to be able to take advantage of this feature in the latest Nvidia drivers, you need up-to-date dependencies (such as Randr 1.4, Xorg 1.13 - that's what the initial Nvidia release notes mention, but it seems you actually need 1.14 -, Linux Kernel 3.9 with some special flags enabled), as well as a custom xorg.conf file and some other bits.

That means that out of the box, the only Ubuntu version that can use this initial Optimus support in the Nvidia graphics drivers is Ubuntu 13.10 Saucy Salamander, but even in Saucy, you need to configure some things to get it to work.

If you're using Ubuntu 13.10 Saucy Salamander or newer, things got a lot easier and you don't need to configure anything to be able to take advantage of this Optimus feature in the Nvidia graphics drivers 319.12+: a package called "nvidia-prime", which comes with a set of tools that enable Nvidia's Prime on MUXless systems, has been uploaded to the Ubuntu 13.10 Saucy Salamander repositories about a month ago and it has currently reached version 0.4 (released today).