In an important vote of confidence in Apple’s (AAPL) resurgence as a mainstream computing platform, Autodesk (ADSK) announced overnight Tuesday that it is bringing AutoCAD back to the Mac.

AutoCAD is an industrial-strength 3D modeling program for software and engineering design. According to Autodesk, its various Microsoft (MSFT) Windows configurations are used by some 10 million people around the world. The last version that ran native on a Mac was released in June 1992. Autodesk stopped supporting it two years later.

The new Mac version is scheduled to be released in October. It will cost $3,995, same as Windows. But in addition to the desktop edition, Apple will be getting a free companion iOS version that runs on the iPad, iPhone and iPod touch. This will have limited design capabilities, but would allow an architect, for example, to bring drawings to a jobs site without having to print them out.

“Apple is thrilled that Autodesk is bringing AutoCAD back to the Mac,” Apple vice president Phil Schiller said in a news release. “We think it’s the perfect combination for millions of design and engineering professionals.”

Apple sold 3.5 million Macs in the quarter that ended in June and is finally starting to gain some traction in large enterprises. According to IDC, Mac sales last quarter grew 3 times faster in the business market and 16 times faster in government that the rest of the industry.

AutoCAD is widely used in both those markets. According to Amar Hanspal, senior vice president for platform solutions at Autodesk, requests for a Mac version were coming with increasing frequency and could no longer be ignored.

The fact that Autodesk was working on the Mac edition was hardly a secret. More than 5,000 users participated in beta testing. Screen shots and YouTube videos of the program in action started appearing on the Web several months ago.

[Follow Philip Elmer-DeWitt on Twitter @philiped]