Mac OS X:Build from source
There are two different ways of installing Gramps on Mac OS X. The two linked pages provide step by step instructions.
You can install it as a native Mac OS X application which means that Gramps windows have the normal appearance of Macintosh Windows. This choice has fewer dependencies on installing other components. However, it has the disadvantage that drag and drop does not work, and there are issues with mouse clicks going missing, which make it much more difficult to enter information like sources which apply to many different people in your family tree. This is also in some ways a less mainstream approach so it may be harder to find help if you get into difficulties.
The other choice is to install it as a Mac OS X X11 application which means that the Gramps windows have an X11 appearance. You could download and install OpenOffice which is very easy to do and will show you what an X11 application looks like. Installing OpenOffice will not be wasted, because you will need it to be able to open reports from Gramps. Installing Gramps as an X11 application is achieved by downloading and installing the packages on which Gramps depends using some software called fink. The process is a bit longwinded, but most of the features of Gramps work, and drag and drop and mouse clicks work very well. If you choose this route, you may be able to get some help both from the Gramps community and the fink community.