Like the previous Clonk titles, OpenClonk offers countless possibilites to create your own scenarios, objects and campaigns. Since Clonk 4, one of Clonk's most remarkable features has been it's extensibility. The complete content is scripted in C4Script, Clonk's own powerful scripting language, has been developed further since 1998. Now, it feels pretty much like a typical C-style scripting language. If you know other programming languages, you will have no problem to familarize yourself with C4Script and if you never programmed before, it can be a good introduction and practice to programming.
You may want to develop based on the latest game data there is. See the nightly builds page for the most current builds.documentation is a complete reference for everything you need to know about the script language C4Script and its data structures, how the the game data is organized and about the APIs for e.g. dynamic landscape generation, using the particle or the effect system.
Note that the documentation is also still available in German, however it lacks maintenance, so always refer to the English version for recent stuff.C4 Development Toolkit, or short C4DT, is a plugin for Eclipse. Using Eclipse with C4DT for Clonk development makes it very comfortable as the editor offers many useful features for editing and debugging scripts you might know from other IDEs.