The process for installing the Arduino software on the Mac is a lot easier than on the PC. As before, the first step is to download the file. In the case of the Mac, it is a zip file.
You can now find and launch the Arduino software in your Applications folder. As you are going to use it frequently, you may wish to right-click its icon in the dock and set it to Keep In Dock.
There are many different LINUX distributions and the instructions for each distribution are a little different. The Arduino community has done a great job of putting together sets of instructions for each distribution. So follow the link below and select one of the ten or more distributions on offer.