A Popular Topics query for bbPress. The built in widget will show either 1) recent topics, or 2) topics with the most replies. This queries topics with a minimum number of replies, whose most recent activity ("freshness") is more recent than a variable date (e.g., "1 month ago").

better-popular.php

<?php

/* Create, then reformat a timestamp for as far back as you want the query to go.
'-1 months' = 1 month ago */

$date = strtotime('-1 months');
$noearlier = date('Y-m-d G:i:s', $date);

/* Build the meta arguments */

$metaargs = array( 
	array(	'key' 		=> '_bbp_reply_count',
		 /* At least three replies */
		'value' 	=> '3',							
		'compare' 	=> '>=',),
	array(  'key'		=> '_bbp_last_active_time',
		/* Last activity no further back than the variable */
		'value'		=> $noearlier,					
		'compare'	=> '>=',
		'type'		=> 'DATE',)
	);

/* Create the query */

$query = new WP_Query( array( 
	'posts_per_page' 	=> 5, 
	'post_type'		=> 'topic',
	'orderby'		=> 'title', 
	'order' 		=> 'DESC',
	'meta_query'		=> $metaargs,
	));

/* Printing the list items */
	
if ( $query->have_posts()) : 
    ?><ul><?php
    while ($query->have_posts()) : $query->the_post();
	?><li><a class="bbp-forum-title" href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li><?php
    endwhile;
    ?></ul><?php
endif;

/* Restore original Post Data */

wp_reset_postdata();

?>