sasl - Add support for the Simple Authentication and Security Layer
savedconfig - Use this to restore your config from /etc/portage/savedconfig ${CATEGORY}/${PN}. Make sure your USE flags allow for appropriate dependencies
scanner - Add support for scanner hardware (e.g. build the sane frontend in kdegraphics)
+sctp - Support for Stream Control Transmission Protocol
sdl - Add support for Simple Direct Layer (media library)
seamonkey - Add support for the Seamonkey web-browser
seccomp - Enable seccomp (secure computing mode) to perform system call filtering at runtime to increase security of programs