Select from multiple tables with laravel fluent query builder

Not tested but here is a start

return DB::table('phpbb_topics')
    ->join('phpbb_posts', 'phpbb_topics.topic_first_post_id', '=', 'phpbb_posts.post_id')
    ->join('phpbb_users', 'phpbb_topics.topic_poster', '=', 'phpbb_users.user_id')
    ->order_by('topic_time', 'desc')
    ->take(10)
    ->get(array(
        'post_text',
        'bbcode_uid',
        'username',
        'forum_id',
        'topic_title',
        'topic_time',
        'topic_id',
        'topic_poster'
    ));

return DB::table(DB::raw('phpbb_topics t, phpbb_posts p, phpbb_users u')) 
->select(DB::raw('p.post_text, p.bbcode_uid, u.username, t.forum_id, t.topic_title, t.topic_time, t.topic_id, t.topic_poster'))
->where('phpbb_topics.topic_first_post_id', '=', 'phpbb_posts.post_id')
->where('phpbb_users', 'phpbb_topics.topic_poster', '=', 'phpbb_users.user_id')
->order_by('topic_time', 'desc')->take(10)->get();