Using Meld merging tool on Mac

1. Install XQuartz

2. Install meld with brew

    brew install meld
   

3. Copy PYTHONPATH

    brew info pygtk
   

4. Paste result of (3) in ~/.bashrc or ~/.zshrc

    export PYTHONPATH=/usr/local/lib/python2.7/site-packages:$PYTHONPATH
   

5. Set meld as your default git mergetool

    git config --global merge.tool meld
   

6. Go find your conflicts!

Source: Homebrew/legacy-homebrew#20644

UPDATE (03/14/2015):

For those who have problems in newer versions Homebrew/legacy-homebrew#36824

If you try:

$ brew install meld
Error: No available formula for meld 
Searching formulae...
Searching taps...`

Instead try:

$ brew install homebrew/x11/meld

Alternative method (by @yousseb)

If you want to install Meld with no hassle go to: https://yousseb.github.io/meld/

• An actual DMG file that you can install right away.
• No X required.
• Key mapping is Mac(ish).
• Used Clearlooks + Tango icon theme in the app so that it looks nice.