Atmel START can be used to generate code for AVR devices.
Hardware drivers, middleware drivers and demo applications for AVR devices are collected in the AVR Code framework. AVR Code is tightly integrated into START, which means that the code can be tailored to the users' needs. For instance, instead of using C preprocessor conditional expressions to enable/disable code blocks, disabled code blocks can be entirely removed from the project source which results in cleaner and easier to read code. The integration into START means that software configuration is done in a user-friendly environment and the generated code is tighter connected to the raw hardware, which makes the firmware image much more compact.
AVR Code is the AVR equivalent of ASF4 for ARM devices. AVR devices typically have more limited resources than ARM devices, and this is reflected in AVR Code. Using START to configure an application and export it to the IDE of choice works in the same way for both AVR and ARM devices.
Detailed description of AVR Code can be found in the AVR Code reference manual.