This article is from the Apple II GNO FAQ, by Devin Reade with numerous contributions by others.
A#13.1: There are no GNO-specific debuggers, however there are at least two popular ones that are compatible with GNO. If you are programming in C, it is highly recommended that you purchase "Splat!", written by Michael Hackett of Some Assembly Required. This is also available from Procyon. See also Q#13.2. If you are programming in assembly, it is recommended that you install GSBug. This comes bundled with ORCA/M and is also available for download from the Apple Inc dts ftp site. GSBug has many add-on packages used to increase its functionality. Two of these are Niftylist and Nexus.
 
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