The ASO file extension is used to signify cache files in Adobe Flash. ASO files hold compiled ActionScript byte code, the Flash scripting language. ASO files can be edited with the appropriate software.
An assembly language is a low-level language for programming computers. It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture. This representation is usually defined by the hardware manufacturer, and is based on abbreviations (called mnemonics) that help the programmer remember individual instructions, registers, etc. An assembly language is thus specific to a certain physical or virtual computer architecture (as opposed to most high-level languages, which are usually portable).
The aso file extension is associated with Simply Accounting First Step, an accounting software for small business, developed by Sage Group plc.