Pentaho offers a version of their software with a free, open-source license, however, it may not be suitable to all requirements as free editions offer limited features. They also typically offer a commercially licensed-version which is more feature rich although it is the same code as the open source, but includes support and warranty.
Adopters of Open Source solutions are typically independent software vendors (ISVs) and systems integrators (SIs) who view these solutions to be attractive alternatives to writing custom code.
Organizations who have over a period of time built their Business Intelligence platform using some of the more expensive BI tools have started realizing that, their investment into the licensed tools is contributing significantly to their IT overheads and are now pressed to move towards the open source tools.
One such tools now being embraced by many organizations is Pentaho. Pentaho provides not just ETL but also functionality on the reporting side of things with decent visualization capabilities. It is a complete package. However organizations looking for rich visuals might still prefer an add on reporting and visualization tool being added to their BI technology stack.
For small to mid size organizations looking forward to setting up a basic BI platform should definitely consider Pentaho.
Pentaho is falls under the Visionary bucket in the Gartner report for BI magic quadrant.
For developers the ETL part of the Pentaho tool is pretty easy to learn and work with. The visual part is a little hard to build as compared to other visual tools.