AAX & RTAS are both proprietary formats for Avid's Pro Tools.
RTAS is the legacy format and has been supported from Pro Tools LE 5.x until Pro Tools 10.
It is only 32-bit and not supported by Pro Tools 11 or greater.
RTAS has been deprecated by Avid in 2011.
AAX is the Avid's current plug-in format and is available since Pro Tools 10.3.5.
AAX is also supported by additional software such as Media Composer.
The following products has been released in the past with RTAS support:
Newer products and updates does not support RTAS.