trying to get all tags/multiple taxonomies

I have this line on a plugin called “user submitted posts”:
<?php $tags = get_categories(array('hide_empty' => false)); ?>
This gives me just the default tags and not the custom taxonomies that I want to get.
So I tried to change that into some other hook like get_tags or wp_tag_cloud:
<?php $tags = wp_tag_cloud( array( 'taxonomy' => 'taxonomy1', format => 'list' ) ); ?>
Then I am able to get the specific taxonomy and not the default tags in the system, but I can’t get multiple taxonomies (taxonomy1, taxonomy2, etc..) and I am also getting it as a cloud and not as a simple list. If I try another hook, it doesn’t work but I want to try anything if you have an idea..