We’ve been using Spiceworks to implement the IT Helpdesk process internally. It works great!
Spiceworks can not only track issues but also IT Asset Mgmt. You can check each asset and find out what issues occured on it. Fantastic! The support engineer would never have to ask the user for previous issues and quickly identify the root cause and solve the problem by just glance to the history record.
It may not be fully complied to ITIL process, but it just works for a small company (e.g. under 50).