You can use ShareISDN to share the functions of an ISDN-Card with other users in a network. For example, every person within a company can send faxes, transfer files or access the Internet via one single ISDN-Card. Installing an ISDN-Card in every single computer of a network would give the same result but of course this would be much more expensive and requires a lot more effort (installing the cards, laying cables, etc).
