If you know already, go here for iTop 2.6 documentation wiki !
iTop stands for IT Operational Portal. iTop is an Open Source web application for the day to day operations of an IT environment. iTop was designed with the ITIL best practices in mind but does not dictate any specific process, the application is flexible enough to adapt to your processes whether you want rather informal and pragmatic processes or a strict ITIL aligned behavior.
At the heart of iTop is the CMDB (Configuration Management Data Base), this is originally the first part of iTop that was developed. Then came the tickets and all the derived processes.
The belief behind iTop is that a CMDB must be an operational tool. The only way for a CMDB to be accurate and up to date is to be used day-to-day by the IT teams (support agents, IT engineers, etc.). Moreover, the more the CMDB is integrated with other IT tools (monitoring systems, reporting tools, automated inventory, etc.), the better.
iTop features, what you can do with it:
iTop can be used by different types of persons:
iTop is relying on Apache/IIS, MySQL and PHP: