[senshu]

I thing it was Borland Turbo C++ 3.0 for MS-DOS. It had syntax highlighting, integrated help with full language and API documentation. Which was useful because I didn't have Internet access back then, at the beginning of the 1990's.

I had to buy a new PC with an Intel 386 CPU, and add "extended memory" to run the IDE. It couldn't run with only 640 Ko of RAM.