Many times I am working in offline mode say I MS Word but at that time my email app says that there is new email in my account, many times I also get notification from my social networking accounts too.
Its so annoying as many times you might be working with full concentration and a email notification disturb you. InternetOff is freeware tool which allows you to quickly turn off or on your Internet connection.
If you want to get internet back for a limited time then also you can get it back as it provide option to get back internet for 5 Min, 154 Min, 30 Min or for an Hour, or else you can turn your internet on for full time.
Its an nice app as it is simple to use and freely available.