To use Apple’s Bonjour to chat on Ubuntu is easy. Ubuntu’s build-in Internet application Pidgin can connect you to other Bonjour user.
To launch the application, from the top of your menu bar of your desktop, go to: go to Applications -> Internet -> Pidgin Internet Messenger
An icon like the one in the picture below will appear near the top right corner of your desktop, click on the icon (similar to the one in the image below) to launch the application:
Click on Accounts->Manage Accounts to add your Bonjour account:
Click on Add button, you will see the following screen, from the drop-down menu, choose Bonjour: