mod_myuserdir is an Apache module for dynamically configured mass user dirs that stores all configuration in a MySQL database. It removes the need to have every user in /etc/passwd and does not require Apache to be restarted after configuration changes. It is also capable of changing PHP4 settings such as safe_mode and register_globals dynamically for every user. By default, open_basedir is set to the home directory and safe_mode is on to prevent users from accessing files belonging to other users.
mod_myvhost is an Apache module for dynamically configured name-based mass virtual hosting with PHP. Virtual host configurations and PHP settings are stored in a MySQL database. There is no need to have every vhost in apache's configuration file, or to restart apache after a configuration change. It is able to change PHP settings dynamically for any vhost. By default, it sets open_basedir as the vhost's rootdir, but you can change almost any parameter that exists in php.ini. For example, you can turn on safe_mode or register_globals for a particular vhost.
mod_jail is an Apache module that supports 1.3.x and 2.x branches. It is similar to mod_chroot, but uses FreeBSD's specific system call "jail", which is more secure than chroot. Thus, it is intended to run on FreeBSD only. This module allows you to run Apache in a secure jail easily, without creating a real jail environment containing a copy of /lib, /libexec, /usr/lib, etc. Also, it is able to change the securelevel within a created jail prison.
maildirquotad is used in conjunction with exim. Exim has no builtin facility for checking the quotas of a mailbox at RCPT TO time. And when you have many MX servers and only one mail hub that stores mail data, it became a real problem, for example, if an MX server has received mail but the mailhub defers it because recipient's mailbox is full, despite the fact that the MX server already has said to remote server that mail had been successfully delivered.