CRSX - combinatory reduction systems with extensions. Combinatory Reduction Systems with Extensions (CRSX) is a system available from url{http://crsx.sourceforge.net} and characterized by the following properties: - Higher-order rewriting engine based on pure Combinatory Reduction Systems with full strong reduction (but no specified reduction strategy). - Rule and term syntax based on lambda-calculus and term rewriting conventions including Unicode support. - Strict checking and declaration requirements to avoid idiosyncratic errors in rewrite rules. - Interpreter is implemented in Java 5 and usable stand-alone as well as from an Eclipse plugin (under development). - Includes a custom parser generator (front-end to JavaCC parser generator) designed to ease parsing directly into higher-order abstract syntax (as well as permitting the use of custom syntax in rules files). - Experimental (and evolving) sort system to help rule management. - Compiler from (well-sorted deterministic subset of) CRSX to stand-alone C code.