Collect3[expr, {x, y, ...}] collects terms involving the same powers of monomials x^{n_1}, y^{n_2}, …
The option Factor can bet set to True or False, which factors the coefficients.
The option Head (default Plus) determines the applied function to the list of monomials multiplied by their coefficients.
Collect3[2 a (b - a) (h - 1) - b^2 (e a - c) + b^2, {a, b}]-2 a^2 h+2 a^2-a b^2 e+2 a b h-2 a b+b^2 c+b^2
Collect3[Expand[(a - b - c - d)^5], {a}]a^5-5 a^4 b-5 a^4 c-5 a^4 d+10 a^3 b^2+20 a^3 b c+20 a^3 b d+10 a^3 c^2+20 a^3 c d+10 a^3 d^2-10 a^2 b^3-30 a^2 b^2 c-30 a^2 b^2 d-30 a^2 b c^2-60 a^2 b c d-30 a^2 b d^2-10 a^2 c^3-30 a^2 c^2 d-30 a^2 c d^2-10 a^2 d^3+5 a b^4+20 a b^3 c+20 a b^3 d+30 a b^2 c^2+60 a b^2 c d+30 a b^2 d^2+20 a b c^3+60 a b c^2 d+60 a b c d^2+20 a b d^3+5 a c^4+20 a c^3 d+30 a c^2 d^2+20 a c d^3+5 a d^4-b^5-5 b^4 c-5 b^4 d-10 b^3 c^2-20 b^3 c d-10 b^3 d^2-10 b^2 c^3-30 b^2 c^2 d-30 b^2 c d^2-10 b^2 d^3-5 b c^4-20 b c^3 d-30 b c^2 d^2-20 b c d^3-5 b d^4-c^5-5 c^4 d-10 c^3 d^2-10 c^2 d^3-5 c d^4-d^5