BrandMeister maintains a Last Heard list. This is a real-time list of all activity on the network.

You can find the list heard page at

The last heard page shows all activity worldwide.  You can open the search panel and create a filter to restrict your view to a single master, repeater, talkgroup, call sign, radio ID, and a few other things.

On each row, you may notice a speaker icon in the Destination column.  This is a link to the Hose allowing you to listen to the conversation.