//Requires http://www.jsfromhell.com/Geral/event-listener

//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/forms/auto-tab [v1.0]

autoTab = function(){
	for( var d, f = ( d = document ).forms, i = f.length; i; addEventListener( f[--i], "keyup", function( e ){
		var el, k = String.fromCharCode( e.key ), l = ( e = e.target ).value.length;
		if ( l >= ( e.getAttribute( "maxlength" ) || l + 1 ) && /[\wÀ-ÿ ]/.test( k ) ){
			for( l = k = ( el = e.form.elements ).length; el[--k] != e; );
			while( !(e = el[ k = ++k * ( k < l ) ]).type || e.disabled );
			e.focus();
		}
	} ) );
};

//Requires http://jsfromhell.com/geral/event-listener

//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/forms/enter-as-tab [v1.0]

enterAsTab = function(){
	for( var f, i = ( f = document.forms ).length; i; addEventListener( f[--i], "keypress", function( evt ){
		var el, l, k = evt.key == 13, e = evt.target;
		if( k && !/textarea|select/i.test( e.type ) && !evt.preventDefault() ){
			for( l = k = ( el = e.form.elements ).length; el[--k] != e; );
			while( !(e = el[ k = ++k * ( k < l ) ]).type || e.disabled );
			e.focus();
		}
	} ) );
};

<form action="">
	<p>
	<input type="text" />
	<br /><input type="text" />
	<br /> <input type="radio" name="aaa" /> opção 1
	<input type="radio" name="aaa" checked="checked" /> opção 2
	<br /><textarea rows="3" cols="15">aaaaaa pode dar enter q ele naum pula hahah</textarea>
	<br /><select><option>opção blablablabla</option><option>opção bleblebleble</option></select>
	<br /><input type="text" />
	</p>
</form>


<script type="text/javascript">
//<![CDATA[

enterAsTab();

//]]>
</script>