Alternative opening for e4 players?

What's the best alternative opening for e4 players that doesn't involve 1. e4? Something that offers similar opening themes.

I've read that c4 or Nf3 are both closer to d4 in terms of how the opening play turns out.

Your question has no answer since there are many ways to handle 1.e4 as white.

U have to be more precise on your repertoire for example.

It is too much of a loaded question.  A 1.e4 player can have an aggressive repertoire (Advance Caro, Nc3 or Advance French, Open Sicilian, Evans Gambit, etc) or a positional repertoire (Exchange Caro, Tarrasch French, c3-Sicilian, Exchange Ruy Lopez, etc).

The reason 1.c4 and 1.Nf3 are compared to 1.d4 is because they often transpose to QP openings, particularly the King's Indian Defense as avoiding the transposition leaves White with an inferior or equal at best position.

You are better off understanding the five pawn types of pawn structures (Closed, Mobile, Static, Open, and Dynamic), figuring out which ones you understand best and which you need to steer clear of, and then figuring out your openings from that.

For example, my strongest is the closed center, my weakest is the mobile center, which is why I play the French and King's Indian, and avoid like the plague the Grunfeld and Alekhine.