Linux and Nero AAC
Command Line Interface
While Nero have released a free command-line AAC encoder for Windows, one is not available for Linux.
The Windows executables (neroAacEnc.exe, neroAacTag.exe, etc) can be used in Linux via the use of Wine, a Windows emulator. Users familiar with a command-line interface can use these programs directly by doing something like the following:
wine neroAacEnc.exe -if infile.wav -of.wav
Graphical User Interfaces
An easier long-term solution would be to link in the command-line encoder into a graphical user interface.