*Using a Service Component Example App*

MathSvc.cmp

<aura:component >
	<aura:method name="add" action="{!c.add}" access="public">
        <aura:attribute name="numbers" type="Double[]"/>
    </aura:method>
	<aura:method name="square" action="{!c.square}" access="public">
        <aura:attribute name="number" type="Double"/>
    </aura:method>    
</aura:component>

// Controller //
({
	add : function(component, event, helper) {
        return helper.add(component, event);
	},
	square : function(component, event, helper) {
        return helper.square(component, event);
	}    
})

// Helper //
({
	add : function(component, event) {
		var params = this.getParams(event);
        return params.numbers.reduce(function(total, num){
            return total + num;
        });
	},
	square : function(component, event) {
		var params = this.getParams(event);
        return Math.pow(params.number,2);
	},
    getParams : function(event) {
		var params = event.getParam('arguments');
        if(!params) {
            return [];
        }        
        return params;
    }    
})

UtilityApp.app

<aura:application >
    *Using a Service Component Example App* <br/>
    <aura:attribute name="number" type="double" default="2"/>
    <c:MathSvc aura:id="mathSvc" />
    <lightning:input type="string" label="number" value="{!v.number}"/>
    <lightning:button label="Add" onclick="{!c.add}"/>
    <lightning:button label="Square" onclick="{!c.square}"/>
</aura:application>

// Controller //
({
    square : function(component, event, helper) {
        component.set('v.number',
                      component.find('mathSvc').square(component.get('v.number')));
    },
    add : function(component, event, helper) {
        component.set('v.number',
                      component.find('mathSvc')
                      .add(component.get('v.number')
                           .split(',')
                           .map(function(item) { 
                               return parseFloat(item);
                           })));
    },    
})