Flipboard style tabgroup indicator for iOS. Drop tabIndicator.js into your Alloy lib folder, then add the module tag to your tabgroup and parameters to override the defaults. As you click on each tab, the indicator will slide across. VIDEO https://www.dropbox.com/s/cbw5e1ruksud9uo/tabindicator.mp4?dl=0

index.xml

<!-- note the ONLY change to this is the additional module="tabIndicator" 
attribute + properties to override indicator defaults //-->
<Alloy>
	<TabGroup module="tabIndicator" tabsBackgroundColor="#000" tabIndicatorHeight="1" tabIndicatorColor="white" tabIndicatorWidth="75%">
		<Tab  title="Tab 1" icon="/images/icons/519-tools-1.png" activeIcon="/images/icons/519-tools-1_active.png" color="#555" activeColor="#fff">
			<Window  title="Tab 1" barColor="black" navTextColor = "#fff">
				<Label onClick="openWin1">Tab 1</Label>
			</Window>
		</Tab>
		<Tab title="Tab 2" icon="/images/icons/516-archive-box.png" activeIcon="/images/icons/516-archive-box_active.png" color="#555"  activeColor="#fff">
			<Window  title="Tab 2" barColor="green" navTextColor = "red">
				<Label onClick="openWin2">Tab 2</Label>
			</Window>
		</Tab>
		<Tab  title="Tab 3" icon="/images/icons/522-floppy-disk.png" activeIcon="/images/icons/522-floppy-disk_active.png" color="#555"  activeColor="#fff">
			<Window   title="Tab 3">
				<Label >Tab 3</Label>
			</Window>
		</Tab>
	</TabGroup>
</Alloy>

tabIndicator.js

// put me in /app/lib

exports.createTabGroup = function(args) {

	// create base tabgroup
	var tabGroup = Ti.UI.createTabGroup(args);

	if (OS_IOS) {

		// get the display width and calc the tab width
		var deviceWidth = Ti.Platform.displayCaps.platformWidth;
		var tabWidth = deviceWidth / tabGroup.tabs.length;

		var indicatorWrapper = Ti.UI.createView({
			width : tabWidth,
			height : args.tabIndicatorHeight || 1.5,
			left : 0,
			bottom : 0,
		});

		// create the base indicator, takes args for height, width, color
		var indicator = Ti.UI.createView({
			height : Ti.UI.FILL,
			backgroundColor : args.tabIndicatorColor || "red",
			width : args.tabIndicatorWidth || tabWidth
		});

		// trap the focus event and animate the indicator
		tabGroup.addEventListener("focus", function(e) {
			indicatorWrapper.animate({
				left : tabWidth * e.index,
				duration : 100
			});
		});

		// add the indicator and return the tabgroup
		indicatorWrapper.add(indicator);
		tabGroup.add(indicatorWrapper);
	}

	return tabGroup;
};