libunique lets you send messages with commands to a running instance using unique_app_send_message(). The commands can be either predefined or custom. Some of the predefined libunique commands have equivalents in GApplication. Instead of sending the UNIQUE_ACTIVATE command, call g_application_activate(), instead of sending the UNIQUE_OPEN command, call g_application_open(). The UNIQUE_NEW and UNIQUE_CLOSE and user-defined commands don't have direct replacement at this time.

As a replacement for custom commands, GApplication implements the GActionGroup interface and lets you add a group of actions with g_application_set_action_group(). The actions can then be invoked, either by using the D-Bus interface for GAction directly, or by calling g_action_group_activate_action() from another instance of the GApplication. The GApplication documentation contains an example for using GApplication with actions.

For more complex needs, GApplication supports passing entire commandlines to the running instance.