To use Meld from Cygwin:

Download and install Meld for Windows. If you get “missing MSVCP100.dll”, install Microsoft Visual C++ 2010 redistributable package

Add to Cygwin ~/.bash_profile

alias meld="/cygdrive/c/Program\ Files\ \(x86\)/Meld/Meld.exe"

Open a new Cygwin terminal to use Meld from Cygwin.

Usage

Many use Meld for git mergetool. For Cygwin:

git config --global diff.tool meld
git config --global merge.tool meld

git config --global mergetool.meld.path "/cygdrive/c/Program Files (x86)/Meld/Meld.exe"