API:

No breaking changes to the API since 4.0. Every model created for 4.0 should work without a problem 

on 4.1. See include/ChangeLog for details.

NED:

Deep parameter assignments: It is now possible to assign a parameter of a submodule inside the parent (submodule.parameter = value). Wildcards (like in INI) files are allowed too.

IDE:

The IDE is now based on Eclipse 3.5.1 and CDT 6.0.1.

IDE usability enhancements

•   NED editor 
• palette enhancement (auto sorting, filter, recently used items)
• connection chooser enhancement (supporting connection labeling with @labels property)
• New Parameter editor dialog for channels and modules
• Completion proposals for connection parameters
• visual feedback for looped and conditional connections
• better validation of NED files in the editor
  
  
• Parameter grouping in ModuleHierarchiView

• The simulation launcher now check for errors (and warns if any) before starting a simulation
• Sequence Chart attach vector usability enhancements
• Scave chart-sheet and chart usability enhancements

IDE extensibility

• automatic discovery and activation of eclipse plugins dropped into the project's plugins folder (allows to create project specific IDE extensions)
• support added for creating wizards for simulation projects (without writing java code). See the ide-customization-guide for further info.

TkEnv:

• Two way connections now rendered as a single line (without arrows)
• Enhanced connection layouting for long shaped modules
• Right clicking on a point covered by several objects brings up the popup menu for all of them (not just the topmost one)

Tooling:

• Source files are now compatible with GCC 4.4 version
• Updated MINGW GCC compiler to 4.4 (on Windows)
• Updated MSYS binaries (on Windows)