The iTunes app with its “Internet Radio” feature meets your requirements. Bundled with every Mac. Already knows hundreds of streams, grouped by genre.
You can type or paste the URL for any stream you want. Save that to a playlist for future use.
Retraction: I no longer recommend iTunes for open streaming. Apple is now interested only in selling Apple Music subscriptions.
Apple had previously taken steps to bury the “Internet Radio” streaming feature beneath two layers of user-interface, hiding it entirely from unaware users.
Now in iTunes version 188.8.131.52, when trying to save a bookmark to return to a station, Apple hides the command as a context-click menu item on the "Now Playing" bar… and even worse… when choosing that command, Apple instead tries to sell you an Apple Music subscription.
For details of these problems, see: “Internet Radio” gone from iTunes 12.7 on the sister site, AskDifferent.com.