DoubleCommand 1.7 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free Mac app is an intellectual property of Michael Baltaks. The program lies within System Tools, more precisely Device Assistants.
From the developer:
DoubleCommand is a software application for Mac OS X (a kernel extension) that lets you remap keys. In other words, with this tool, you can change the way your keyboard works. Often used to make a PC keyboard more comfortable with a Mac, swapping the Alt (Option) and Windows (Command or Apple) keys, since they are in swapped positions on Mac and PC keyboards.
You may want to check out more Mac applications, such as Double Commander or KeyRemap4MacBook, which might be related to DoubleCommand.