You can download the free ASE Developer Edition from the SCN Developer Center for ASE (http://scn.sap.com/community/developer-center/oltp-db).
Note that there's also a free ASE Express Edition, but this is available only for Linux while the ASE Developer Edition is available on various platforms.
The other advantage of the Developer Edition is that it you can enable most ASE options; for the Express Edition, you cannot.
For ASE documentation, go here: http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.help.ase.15.7.sp100/doc/html/title.html