MSCGen for Mac OS X

In order of preference, I suggest:

Install using Homebrew (assumes you have previously installed Homebrew):

brew install mscgen

Another way is to use Macports, but Macports still uses version 0.18:

sudo port install mscgen

And finally, I compiled mscgen 0.2 on Mac OS/X 10.7.3 just now:

wget http://www.mcternan.me.uk/mscgen/software/mscgen-src-0.20.tar.gz
tar xvfz mscgen-src-0.20.tar.gz 
cd mscgen-0.20/
./configure
make
make check
sudo make install # conflicts with Homebrew

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