Sahi is a test automation tool for graphical user interface. You must have heard about Selenium. The purpose of both of them is similar - reduction of tedious, repeatable tasks in testing. For example, when a new feature is developed, it is tested. But if any other changes in the code happen, the feature should be tested again to make sure nothing was broken (regression testing). Clicking the same steps by human again and again is not a good way of spending time and money. Sahi allows to automate repeatable tests.