Plesk is a hosting automation solution that gives hosting providers full control over the managed Web hosting servers and simplifies setup and management of user accounts, Web sites, and e-mail accounts.
Plesk is stable, secure and reliable, and the main benefit of using Plesk is that it will save you and your technical staff much time and effort: all your customers (and customers of your resellers) will have personal isolated control panel environments and will be able to manage their sites and e-mail accounts on their own.