Most regulated forex brokers these days offer some kind of of web-based trading platform to their clients, whether it is a platform built from scratch for the web, or if it is a desktop platform with a modified version for web use. Examples of the latter type of trading platform includes the web versions of MT4 and MT5.
Web-based trading platforms have several advantages over traditional downloadable trading platforms. Perhaps most importantly among these is the fact that all work done on a web platform automatically gets saved in the cloud. This means that a trader can work seamlessly with for example chart analysis across several different devices without the risk of losing any of his work as he moves from one device to another.