STklos is a Scheme implementation that succeeded STk. It is an interpreter based on an ad hoc virtual machine which aims to be fast as well as light. In addition to implementing most of R5RS, STklos supports: * an object system based on CLOS with multiple inheritance, generic functions, multimethods and a MOP * a module system * regular expressions via PCRE library * a simple foreign function interface via libffi * a number of SRFIs Additional libraries are available through its package system ScmPkg.