Application threads are supported. After sending a stop signal to the application (Stop or F9), a random thread will be selected in HDevelop. Stepping over the last line of a procedure switches threads if another stopped HDevEngine thread is waiting. In case HDevEngine stops due to a breakpoint or an error, HDevelop will automatically switch to the corresponding thread.
The normal thread view in the dialog Execute ▹ Thread View / Call Stack is not available, but threads can be switched from this dialog by clicking the button Show Application Threads....
Please note that subthreads started with par_start cannot be debugged.