SIMPL (Synchronous Interprocess Messaging Project for Linux) is discussed at many different levels. At its most fundamental, SIMPL is a set of library functions which allow the passing of encapsulated messages between cooperating processes. On another level, SIMPL is an active open source project which began over a decade ago. Over the years this project has accumulated an extensive body of sample code and extensions. SIMPL is also a great way to design software applications where complexity is encapsulated in separate, easily testable, readily extendable modules. The current state of software development is compared to the hardware world before the advent of integrated circuit chips. The term softwareIC is coined to describe the software equivalent of the integrated circuit. The SIMPL toolkit, along with tokenized messaging and the SIMPL testing framework is shown to be a great way to build these softwareICs. Several are illustrated throughout the book.