Smallworld had a suite of tools called Magik Studio for pre 4.0 releases. The debugger worked similarly like other programming language debuggers. The biggest thing was you had to compile the method after magik studio was loaded. This was my favorite debugger…. I believe it was written by Ken Korsmit. I would love to get that working under 4.X.
Smallworld had sw_dev_tools module that allows you to debug magik code. You had to request it from your support representative to get it as it wasn't "officially" released
4.1 & 4.1.1
Smallworld included the sw_dev_tools as part of the standard deliveries. It allows you debug methods.
Click here for some code snippets of use.
MDT Project Is a pretty interesting tool. I have only seen it demonstrated at the Smallworld Conference.