One thing Nokia is known for in the smartphone world is the cameras it builds into its devices. The PureView with Carl Zeiss lens has proven a more than capable shooter, and those who have an eligible device -- 920 (and variants), 1020 and 1520 -- have had access to the Nokia Camera for sometime now. But Nokia is now rolling it out to all Lumia devices, though it is in beta form.
You do have to have installed the Amber update, which is setting the bar relatively low, as most everyone should have this by now. It is pre-release software, so the Finnish company offers a bit of a warning to prospective users -- "in this beta trial you will get frequent updates with the latest features and improvements, but there could be bugs. This trial is aiming to collect feedback on overall usability on all Lumia phones and to verify the latest fixes and improvements we do".
If you want to grab the Nokia Camera, but could not previously do so, then head to the Beta Labs, linked below. The new support adds the Lumia 520, Lumia 521, Lumia 620, Lumia 625, Lumia 720, Lumia 810, Lumia 820, and Lumia 822 to the previously supported phones. The app is free and, having been using it for sometime, I can testify that it makes a big difference over the built-in Windows Phone camera.