OLAP and MDX

I've been poking around looking at techniques for database design, because every actual application I go to design these days essentially starts with a database.  (More on this later.)  (Well, and previously, of course.)

But while looking at these things, I ran across the concept of OLAP (online analytical processing), which is essentially based on the concept of keeping a matrix of figures of high dimensionality available for fast ad-hoc querying.  The query language usually used is MDX.  (MultiDimensional eXpressions.)

I don't have much specifically to say about this, just wanted to note that OLAP exists but is apparently entirely dominated by big players.  Which is interesting.  Is it because only the big players can market successfully to the corporate buyer most interested in OLAP, or because OLAP just isn't that interesting to the open-source world?  (I find the latter improbable, so maybe there's a market for low-price OLAP.)