Online radio streaming app iHeartRadio has just made good on its promise to add support for CarPlay, Apple's new car infotainment system. But, it's not the only app joining Spotify on CarPlay today -- Rdio, a free music streaming service with offline playback, is tagging along. By introducing optimized apps for Cupertino's car platform, both online services make it easier for users to navigate their interfaces on an onboard screen. Sadly, there are very few people who can actually enjoy the updates right now, as CarPlay's only available on Ferrari FFs and select Pioneer in-dash systems, though most automakers promise to load it on their vehicles' entertainment systems in the future. Other web services also vow to eventually introduce optimized apps for the platform, including CBS News Radio and, of course, Beats Music.