No, at least not any more.  Early online casinos all used downloadable software because the web was brand new and web browsers just didn’t have enough features to play games on websites.  Even today some online casinos are software based, and you must download and install their online casino software or app to play their games.  However, most internet casinos these days offer browser based games that require no download or instalaltion.  These web-based environments offer the same ability to open an account, deposit money, and play the games.  They are also ideal for gamblers looking to use mobile devices and operating systems other than Windows, like Android, Mac, ChromeOS, or Linux.