<ul id="catnav">
<?php
global $post;
foreach((get_the_category()) as $category){
echo $category->name."<br>";
$category = $category->cat_ID;
$myposts = get_posts(array('numberposts' => -1, 'offset' => 0, 'category__in' => array($category), 'post_status'=>'publish', 'order'=>'ASC' ));
foreach($myposts as $post){
setup_postdata($post); ?>
<li>
<a href="<?php the_permalink(); ?>">
<?php the_title(); ?></a>
</li>
<?php
}
}
wp_reset_query(); ?>
</ul>