Please follow the appropriate setup instructions for your operating system to install Mercurial and/or TortoiseHg as well as KDiff3.
If you don't already have one, please create an account for yourself on Bitbucket.
Install Mercurial and KDiff3 by downloading and running the TortoiseHg installer.
Optional: If you want to use a more Unix-like command-line shell, install Git for Windows, which includes a Bash emulator, by downloading and running the installer.
Install Mercurial by downloading and running the installer for your version of OS X from the downloads page. Also, please install the KDiff3 diff and merge tool.
Optional: The version of Mercurial above is for the command-line (Terminal). If you prefer to use a mouse and windows graphical user interface (GUI), you can download and run the TortoiseHg installer.
If Mercurial is not already available on your machine you should be able to install it via your system package manager. Also, please install the KDiff3 diff and merge tool. It should also be available via your package manager.
Optional: The version of Mercurial above is for the command-line (Terminal). If you want to try a mouse and windows graphical user interface (GUI), you can install TortoiseHg. Please see the downloads page there for instructions for your flavour of Linux.