Gitter is available in all modern browsers as well as apps for desktops and mobile phones.
Our efforts are focused on the webapp which is the backbone of the mobile/desktop apps but mainly focused on the web experience. There are a number of bugs in these desktop/mobile clients and they spread the Gitter team too thin for us to give them proper attention. The apps are open-source if you want to tackle something particularly annoying to you. (desktop, iOS, Android)