I'm looking for a tool to create web-based OLAP views --something like Microsoft BI Portal or Oracle Discoverer. Something that can create web-based pivot tables, pie charts, and such, while taking the data from OLAP cubes.

Is there any open source software for such purpose? And what would you suggest?

Also, what is the best open source OLAP server out there? (the open source equivalent to Microsoft Analysis Service) How about postgreSQL? Does it come with 'cube server' feature like Microsoft Analysis Service to Microsoft SQL?