As the question says how to install Github for Windows without an internet connection? If it is not possible then is there some alternative client with the following features:<
"GitHub for Windows" is one of those magical/annoying ClickOnce apps. They are ideal for apps that tend to require online to operate (like posting to an online source control website...)
Other then the magic "clone to windows" feature from the website, and the self contained SSH auto-management (also semi-annoying), there isn't anything special about it other then being "pretty".
If you really really need offline work, or behind proxies, get something else. GitExtenions is great integration into windows context menus, and a great repo manager, and a not too confusing add/stash/commit interface. It reminds me very much of TortoiseSVN.
MSysgit is also an option for GUIs, but is a bit more crude (it looks very 16bit app'ish). Personally, I'd rather use the commandline then it, but thats me and my choices.
Oh, and lastly, in less then 10 seconds and 1 google search, I found how to set GHfW to work through a proxy using the standard .gitconfig