- "Sublime Text" for the text editing
- "Beyond Compare" for all the diffing
- "Paint Shop Pro" (8 or 9) for the graphics
None of these are free software, but I bought the licences a long time ago, and they work well for me, that being said the OSDK does not really care, as long as you can save good old text files and png images, it just works

Regarding the BASIC syntax coloring, it's just a quick hack that does not work very well because most syntax coloring systems expect tokens to be separated by either punctuation or whitespace. They don't like things like IFA=BTHENPRINTC!
Maybe I should do a few videos on how to use the OSDK, pictconv, filepack, etc...?