MS Silverlight is a browser plugin for Internet Explorer, Chrome, Firefox, Safari etc. It was developed by the clever folks at Microsoft and works the same way as Flash, which you may have seen on the web.
It allows feature-rich internet applications (a lot smoother and more powerful than normal web applications) in the web browser. It also means that any device that has a compatible browser can run Silverlight and therefore could run PokerDIY Tourney Manager.
PTM is written in Silverlight which means we can take advantage of this web platform and create a great online app that can also be downloaded with ease.
You can read more about MS Silverlight here and check if you have a compatible computer/device here. If you are running the latest version of Silverlight then you should be able to run PTM.