There are quite a few scheme implementation for Java platform, they are used for scripting and prototyping of Java applications. There exists continuation-based web framework for J2EE in scheme, called SISCWeb.
Guile scheme is used as scripting language in some GNU apps - GnuCash for example is mostly written in Scheme.
Also TinyScheme is used as scripting language for GIMP and some variations of it are used in embedded systems.
