Let A be a non-commutative algebra and let X be some geometric space (such as a topological space or an algebraic variety or scheme). Is there a notion of cohomology ring of X with coefficients in A? What is the correct set up to consider cohomologies with non-commutative coefficients? 


If a topological group $G$ acts on a space $X$ one can construct its equivariant cohomology ring $H^\*\_G(X)$ (say with coefficients in $\mathbb{R}$). Is there a notion of equivariant cohomology for $(X, G)$ with coefficients in a non-commutative algebra $A$? 



Cohomology ring with non-commutative coefficient ring

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Yes, and nothing new is needed. The underlying additive group of $A$ is abelian so you take cohomology with coefficients in that abelian group; then the multiplication on $A$ is a bilinear map $A \times A \to A$ which induces a map 


$$H^n(X, A) \times H^m(X, A) \to H^{n+m}(X, A)$$


in the usual way. That is, the construction is exactly the same as for cohomology with coefficients in a commutative ring; commutativity of the multiplication is not actually used in the construction. So this isn't actually "nonabelian cohomology" in the sense that term is usually meant. 


