"Groupware" is a not-well-defined biz talk term that usually refers to anything that can be used to boost the collaboration among workers.
Typically, groupware uses company intranet/LAN and has a central server where that's used using either a web browser or a specialized client.
Typically, groupware applications include E-mail/instant messaging, bulletin boards, shared calendars, directories, document archives, databases and such. Usually, these are platforms that can be somehow extended.
It'd be also worth noting that groupware is usually sold to companies as expensive "solutions" - yet, many of the components can be implemented in intranet using open-source software. Want E-mail? Just set up normal Internet E-mail (optionally with transparent encryption). Want message boards? Set up a nntp server like Leafnode or INN and create a few local newsgroups.
There even are complete groupware suites available (like phpgroupware).