Note particularly:

- The macro system has been completely rewritten and is now fully hygienic with highlevel R5RS "syntax-rules" macros and low level "explicit renaming" macros that allow full control over hygiene; "define-macro" is not available anymore

- A module system has been implemented that fully supports hygienic macros and integrates with separate and cross compilation; module- and syntax meta-information is not retained in compiled run-time code, unless explicitly enabled by the user

- Experimental support for cross-module inlining

http://groups.google.com/group/comp.lang.scheme/browse_thread/thread/ 3d248d275f929b97#