Does RiffWorks run on the new Intel-based Macs?

From Guide

Yes. RiffWorks Standard is a Mac OS X Universal binary and will run on all intel Macs.

However the version of Amplitube LE included with RiffWorks Standard is not yet available as a universal binary. When it is available from IK Multimedia, the new version will be made available from your store downloads page.

See System Requirements for more information.