Prototyping future Internet technologies is an important but complicated task, mainly caused by incompatibilities to existing systems and high implementation complexity. To reduce these problems, we have developed the Future Internet Toolbox (FIT), consisting of four frameworks that cover data transport, information-centric networking, naming, and name resolution. These frameworks can be used separately or can be combined to a large testbed, covering many aspects at once. Experience has shown that FIT not only simplifies our own prototyping activities but is also useful for other projects due to its generality. Key words: Future Internet; network; testbed; framework; prototype; information-centric; data-centric; transport; naming; name resolution