The stonewall attack for white is perfect. Hardly ever any new red hot theory to learn.
Versatile Openings

Thanks knightassassin. I have read that the modern defence is solid against d4 and e4 openings. Can anyone confirm this from their own experience?

Yes, I can confirm from my own experience that the Modern Defence 1...g6 2...Bg7 is good against 1 d4 and 1 e4.
Certain defenses (The Pirc, The King's Indian, or Modern) allow White to build a classical center within the first few moves, and so can be classified as "systems" against either 1.e4 or 1.d4. (If course, playing 1...Nf6 in response to 1.e4 will usually not transpose into a King's Indian.)
Some flexible Openings for White include: The English (1.c4), the Reti (1.Nf3), and 1.b3 (Not sure what this is called!) Flexible Openings for Black: The Modern (1...g6), 1...e6 (Can transpose into tons of different defenses.), and 1...d6 (Again, can transpose into many defenses easily.)

Basically all those non-mainline d4 systems are easy to learn and playable.
As black, the Scandinavian and the Queen's Gambit Declined are both simple enough to learn and totally respectable.
The hedgehog and the hippopotamus are versatile openings: you can play these as black against 1 e4 as well as 1 d4 and you can play these in reverse as white.
https://en.wikipedia.org/wiki/Hedgehog_(chess)
https://en.wikipedia.org/wiki/Hippopotamus_Defence
I’m a club player. These opening where in vogue in the 1920s -1940s and where played by the 2600s of the day…. way way way stronger than I’ll ever be. If they where good for them .. they are definitely good for me.

English opening, reti opening, KIA, and the nimzo larsen attack for white are some very versatile openings, ESPECIALLY the reti, which can also transpose into the KIA and english the turn right after. (1. Nf3 Nf6 2. c4 and we are in english. 1. Nf3 d5 2. g3 and boom KIA.)
Are there many simple yet versatile openings that provide an opportunity to reach a balanced middle game without having to learn a ton of theory? I am looking at the Torre Attack presently and would like to learn an e4 opening with these qualities as well. Any suggestions?