MzScheme is an implementation of the Scheme programming language for
Windows 95/98/NT, MacOS, Unix, and BeOS. MzScheme is R4RS-compliant
(including the full numerical tower) and nearly R5RS-compliant (some macro
support is lacking).

 MzScheme also provides: 

- Pre-emptive threads for all platforms 
- Generative structures (a.k.a. record datatypes) 
- Built-in exceptions; each primitive error raises a specific exception 
- First-class compilation units (modules) for organizing program components 
- A class-based object system reminiscent of C++/Java 
- Built-in regular expression matching tools 
- Simple TCP communication support on all platforms 
- Portable filesystem access procedures 
- Platform-specific process control, including AppleEvent support