Small Openings Like the Catalan?

So I have recently been wondering are there any other 'small' openings such as the Catalan which have a good amount of theory? Big openings are openings like the Ruy Lopez, Queen's Gambit, or Italian Game. Anybody know any small openings like the Catalan which have a good amount of theory?

Also I would consider the Four Knights' Game as a 'small' opening with a considerable amount of theory

I think they are called "big" openings because they are played often and studied by grandmasters, who post the stuff they find. So it is often considered and easy to play, but is also often studied by your opponent. So "big" may mean "fmaous", or "well known"

Well I am talking about openings which are discussed but not as much as 'big' openings such as the Ruy Lopez or Queen's Gambit

And those openings are maybe even not considered to be 'ideal' for white/black

Vienna game imo for e4. d4, maybe like the Veresov attack i guess

thanks @DaBabysSideTing

I would agree they are good openings, which I would consider 'small', and I would also say that they may not be 'ideal' but they are very good.

The Ponziani Opening also seems like a 'small' opening but a good one.

tbf there are a lot of cool, unstudied openings in the Vienna

like there are so many variations in the Vienna that can cater to any playstyle

I know that is what makes it a good opening, while not being nearly as popular as main-stream openings. I also like the Nxe4 line that you showed, it has the best name ever: The Frankenstein-Dracula Variation.

I don’t think the Catalan is small. 

theres not a lot of extreme theory involved, just a lot of general ideas in the open and closed variations, qa4+, ne5, qc2, nbd7, etc etc

True.

I would consider the Catalan as 'small' because the Catalan is not something every chess player knows. And As DaBabysSideTing said there is not nearly as much theory as the Queen's Gambit involved. 

Also maybe the Torre and Trompowsky would qualify.