Edit: In case you actually do want to play with it, Ingres is now Actian IngresX. Though I'd recommend thinking about what could have been instead of actually spending any time fighting with and configuring Ingres.
The latest iteration is actually called 'ActianX', and it's a continuation of Ingres plus support for column-based tables from the 'Vector' product acquired by Actian.
QUEL is still there, but its functionality has been frozen for years and, in terms of bells and whistles, is way behind modern SQL.
If you do want to try it, I had no trouble installing it on my home Ubuntu system a couple of years ago. Ingres is pretty easy to use in some ways. If you want to make a database, you just type "createdb mydatabase" at the command line.
Uh, it's nice to see the name Actian come out for once.
My previous employer used Versant by Actian (now called Actian NoSQL) heavily.
It's much more of a NoSQL database: it's a real object oriented database. You don't store tuples, you store objects. You don't make queries with selection and projection, you make a cut of a graph of objects.
It's insanely fast, multithreaded, has very good tooling, scales vertically very well, can do online schema evolution (class definition evolution, really).
Sadly it's almost impossible to scale horizontally (I'd be glad to be proven wrong).
It's basically what the industry needs to avoid the object-relational mismatch: an object oriented database.