We have a client that has Oracle Standard, and a project that would be ten times easier addressed using OLAP. However, Oracle only supports OLAP in the Enterprise version.
Migration to enterprise is not possible
I'm thinking of doing some manual simulation of OLAP, creating relational tables to simulate the technology.
Do you know of some other way I could do this? Maybe an open-source tool for OLAP? Any ideas?
You can simulate OLAP functionality using client side tools pointed at a relational database.
Personally I think the best tool for the job is probably Tableau Desktop. This is an amazingly sophisticated front end analytics tool that will make your relational data look multidimensional without much effort, and the tool itself is really mind blowing. They have a free trial so you can take it for a spin. We use Tableau heavily for our own analysis and have been very impressed. Of course, this tool also works with multidimensional databases as well, so if you end up with some cubes at the end of the day you can continue to use the Tableau front end.
As for open source, you could try out Palo - an open source MOLAP server and Excel front end.
If you are interesting in building your own reporting front end and use .NET there are a number of components (such as the DevExpress PivotGrid or the several tools from RadarSoft) that will do the same thing, but will require some elbow grease to get wired together.