Gitter is available in all modern browsers as well as apps for desktops.
The above Mac installer is a signed version of 1.177 (backed by Safari). For an unsigned 5.0.1 installer (backed by NW.js), click here to download. Mac users on 10.9 or lower, download here.
We also have a sweet little IRC bridge.
The dedicated Gitter Android/iOS apps are no longer recommended and are officially deprecated. For Android/iOS, we bridge all public rooms over to Matrix, so you can use any Matrix client like Element (Android) or Element (iOS) to access those rooms.
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)