Skype, Ventrilo and FaceTime let users voice chat for free. While the first two are available for both Windows and Mac OS X systems, FaceTime is only available for Mac OS X.
Designed to work as an integrated part of the Windows operating system, Skype is available both as a desktop program and a Web application. Skype functions similarly to mobile phones. Users call each other to initiate voice chat and can have conference calls with up to 25 people. Skype also supports video chat and can directly call mobile phones. Although calling phones normally costs money, Office users can make free calls for up to 60 minutes every month.
Ventrilo is an advanced voice chat application that can provide voice chat with multiple channels at once. Gamers often use Ventrilo in multiplayer games to discuss game tactics in real time. The application supports both chat rooms and private conversations. Ventrilo provides password protection to chat rooms, works on dedicates servers and allows remote administration.
Initially intended for video chat, FaceTime gained voice chat capabilities in a software update. The application comes pre-installed in Mac OS X computers and iOS devices. FaceTime also supports conference calls and can respond to voice commands. IOS users can instruct Siri to make a call in FaceTime.
Skype and FaceTime are also available for mobile devices. The applications support cross platform communication. For instance, a Windows user, an Android user, a Mac OS X user and an iPhone user can have a conference call in Skype. Likewise, desktop and mobile Apple devices can establish voice chat through FaceTime.