Gradio is described as 'Find and listen to internet radio stations' and is an app in the Audio & Music category. There are four alternatives to Gradio for Linux and Android. The best alternative is RadioDroid, which is both free and Open Source. Other great apps like Gradio are Radiotray-NG (Free, Open Source), Shortwave (Gnome) (Free, Open Source) and Goodvibes (Free, Open Source).
Look up online radio streams at RadioBrowser and listen to them. RadioBrowser is a wiki like aproach to collect as much online radio stations as possible. Every one can help by not only adding new stations but also tagging existing ones.
The successor of Gradio, Shortwave will include all important Gradio features and more. Discovery and search radio stations listed in the radio-browser.info database, listen to them, automatically record songs, and stream to Google Cast-enabled (Chromecast) devices.