Omega Drivers

Omega Drivers were unofficial, third-party device drivers for ATI and NVIDIA graphics cards, created by Angel Trinidad. They differed from the official drivers in that they offer more customization and extra features. They are compatible with some ATI graphics cards and some NVIDIA cards that use Detonator drivers.
The drivers are tweaked versions of those officially released by ATI and NVIDIA, mainly using registry tweaks and offering an alternative installer. They are not custom drivers compiled from source code.
From the website:

WWW Official Site

ATI driver features

The Omega ATI driver is based on ATI's Catalyst drivers. The driver is particularly notable for resolving 3D compatibility problems affecting past versions of the ATI drivers and some AGP cards.
The driver includes various third-party utilities including 'MultiRes' and ATI Tray Tools tweaking utility.

Reception

The drivers are recognized by ATI as the best alternative drivers on the Internet according to Terry Makedon:
NVIDIA has previously attempted legal action against some versions of Omega Drivers; the company has since allowed Omega Drivers for NVIDIA cards to be made.

Branding

Recently, AMD began offering an upgraded driver, known as the Catalyst Omega driver. AMD claims that the change in brand is due to the significant feature additions - and has not mentioned the existence of Omega Drivers. Omega Drivers has noted it is not affiliated with the AMD-distributed Catalyst Omega driver.