What is the difference between apex:actionfunction and apex:actionpoller in Salesforce? Is there any way to do the same functionality of apex:actionpoller?

apex:ActionSupport: This component adds Ajax request to any other Visualforce component. Example : Commandlink button has inbuilt AJAX functionality however few components like OutputPanel does not have inbuilt AJAX capabilities. So with the help of this component, we can enable AJAX.

<apex:outputpanel id=”counter”>
<apex:outputText value=”Click Me!: {!count}”/>
<apex:actionSupport event=”onclick” action=”{!incrementCounter}” rerender=”counter” status=”counterStatus”/>
</apex:outputpanel>

apex:ActionPoller: This is timer component which can send AJAX request on pre-defined interval. Minimum interval is 5 sec and default is 60 sec.
<apex:actionPoller action=”{!incrementCounter}” rerender=”counter” status=”counterStatus” interval=”50″ />