ManOpen 2.6 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. The software lies within Developer Tools, more precisely IDE.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The application's installer is commonly called manopen-2.5.1.dmg. The most popular versions of the tool are 2.6 and 2.5. This app's bundle is identified as org.clindberg.ManOpen. The actual developer of this free Mac application is clindberg.
From the developer:
ManOpen is a MacOS X GUI application for viewing Unix manual pages, which is the standard documentation for Unix command line programs, programmer libraries, and other system information. It can open files directly or be given titles, in which case it will display the output from the `man' command-line program. An apropos interface is also provided, which is basically a quick-and-dirty search of the man page databases.
You may want to check out more software for Mac, such as JProfiler, Pashua or Eddie, which might be similar to ManOpen.