HotMail is Microsoft's free web-based e-mail service. It is integrated with some of Microsoft's other web services, like MSN and Messenger.
See http://www.hotmail.com for more information.
When MSFT bought HotMail back in 1997 (from uunet?) it was running a FreeBSD/Apache front end and Sun Solaris for the back end. After a couple of aborted attempts to shift it to NT, the front end (but not the back end) was finally migrated to Windows 2000 over the course of several months in 2000. To date there is no indication that the Sun Solaris back end has been replaced. -- StevenNewton