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:<
This is the answer I received from the support today (2015-06-30):
Unfortunately we do not have a standalone installer at this time. GitHub for Windows makes use of Microsoft's ClickOnce technology for installation and updates.
We are currently working on an open source replacement for ClickOnce here:
https://github.com/squirrel/squirrel.windows
Once that technology is complete and ready for use, we hope to switch GitHub for Windows to use that. It would allow for a standalone installer.
In the meantime, you can find a list of alternate GUIs available here:
http://git-scm.com/downloads/guis
For the current version (as of June 2017) of GitHub Desktop (windows), you can go to https://github-windows.s3.amazonaws.com/standalone/GitHubDesktop.exe for the standalone, offline installer.
For GitHub Desktop (beta), the team is also working to make it an offline installer hopefully by version 1.0. Currently the installer has some issues that prevent it from installing successfully.
"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