Muir is described as 'mobile browser testing app without all the strings of cloud based suites. Simply download the desktop app, install the client on your mobile devices, and get to work' and is an app in the Development category. There are three alternatives to Muir for a variety of platforms, including Mac, Windows, Online / Web-based, Android and iPad. The best alternative is Browsersync, which is both free and Open Source. Other great apps like Muir are Ghostlab (Paid) and DOMScope (Free).
Whether you want it or not, your site is going mobile - every day. Use Ghostlab to make sure all your users get the same neat experience - whatever operating system, browser or smart phone they are using.