RISC OS SignalBox Simulation RISC OS
http://www.svrsig.org/

Loading additional boxes:

Typing 'L' opens an explorer window of the directory 'SIGBOX' and displays all files of type '.BOX'. Select one in the normal way and this box will be operated. In the unregistered version, additional boxes may not be loaded and in the free version only skeleton files are provided to illustrate the boxes available - additional boxes must be purchased for a particular user and will be keyed to the registered six digit key. Next step.

step 8