Buck is the simplest complex collaboration tool you could imagine. And everything deletes itself - just as in real life :)

initial setup instructions:

1) elasticsearch 0.15.0, apache with mod_rewrite and php >=5.3.0
2) php -f elasticsearch_setup.php
3) fill out email/password/domain in secret.php (superadmin needed for the provisioning api)
4) check your webserver or get cracking with the REST API