MyAppAction footer extension (tested on Sugar 7.5, 7.6)

addFooterAction.ext.php

<?php
//  Append new View to Footer layout's list of components
$viewdefs['base']['layout']['footer']['components'][] = array (
    'view' => 'my-app-action',
);

my-app-action.hbs

{{! 
    Define HTML for our new button.  We will mimic the style of other buttons
    in the footer so we remain consistent.
}}
<button data-action="chat" class="btn btn-invisible" aria-label="{{str "Chat"}}" role="link" type="button">
    <i class="fa fa-comments icon-comments"></i><span class="action-label"> {{str "Chat"}}</span>
</button>

my-app-action.js

({
    events: {
        //On click of our "button" element
        'click [data-action=chat]': 'chat'
    },
    // tagName attribute is inherited from Backbone.js.
    // We set it to "span" instead of default "div" so that our "button" element is displayed inline.
    tagName: "span",
    chat: function(){
        // Use Sugar 7 API to pop one of our standard alert message boxes.
        app.alert.show('myapp-chat-alert', {
            level: 'info',
            messages: 'Send a chat message!',
            autoClose: true
        });
    }

})