Mac OS X comes with a lot of fantastic stuff built-in, like Java, Ruby, Python etc. The downside to this is that users tend to stick with the stock installs of those items and never upgrade them, which can leave them a long way behind the curve. I just ran into that problem when trying to install the latest version of Ramaze (my favourite Ruby web application framework) from the official gems. The IRC channel #ramaze was useful as always and provided the solution. The problem is that rubygems on OSX 10.5 is old and tired, but you can tell it to install a very specific version of innate that sorts it out. So from scratch, assuming Mac OS X 10.5 with the stock Ruby 1.8.6 install:

Obviously as new versions of innate and ramaze come out, the exact version of innate required will change. You can tell which verison you need by trying the ramaze install and looking at the error message.

Update: Actually now Ramaze and Innate 2009.05 have been released, it seems things work just fine without any special incantations. So you can just sudo gem install ramaze and you're away.