Kerbal Space Program 1.1.3 for Windows, Mac OS X, and Linux. Archive format is 7zip. To play, simply extract the "Common.7z" file and the file appropriate for your OS - either "Windows.7z", "Windows64.7z", "Mac.7z", or "Linux.7z".
Total extracted data for a single OS is about 2.2GB. Feel free to extract multiple OS files on top of each other - they don't conflict (the 32 bit launcher is included in both Windows and Windows64, but are exactly the same so just overwrite).
Have fun :D
Executables aren't compressed so all file hashes should match exactly to the official release - no viruses! (if they were compressed further, another 80MB could have been saved)