Very flexible and widely used reporting environment, but you will need to buy the commercial product ActuateOne to get bells and whistles (Dashboards, ad-hoc reporting etc).
Actuate claim that Eclipse BIRT is the most widely used open source BI suite. As the name suggests it runs on the Eclipse IDE platform and provides various reporting and data visualisation tools. This provides the foundation for report design and viewing.
The BIRT engine is at the heart of this offering, and this is a collection of Java classes and APIs which execute BIRT reports and generate them in appropriate formats. Reports include lists with grouping and calculations, charts (pie charts, line and bar charts etc) which can be rendered in SVG and support events to be interactive, crosstabs, documents (textual data) with embedded lists, charts etc, and compound reports (aggregated and embedded reports).
Actuate sell a version of BIRT on steroids called ActuateOne which includes BIRT Design (for report design), BIRT iHub and BIRT User Experience (Ad Hoc Reporting, viewers, Dahsboards, mobile support and Data Analyzer).