Let $ mathbf {Grp} $ to be the category of groups and $ mathbf {Top} $ to be the category of topological spaces. To each group $ (G, circ_G) $we can associate a topological space $ (G, tau_G) $ the basis of this topology being given by all of the subgroups of $ G $. Call this topology on $ G $ to be his **Subgroup topology** So we get a functor $ mathscr {F}: mathbf {Grp} to mathbf {Top} $ which associates a given group with its. Also note that any homomorphism $ f: (G, circ_G) to (H, circ_H) $ induces a continuous function between the correspondent **Subgroups of Topological Spaces**.

This process looks like a kind of "reverse process" compared to what we do in algebraic topology, especially when we try to associate the fundamental group with a given topological space. In Algebraic Topology in general, we try to find algebraic invariants of a given topological space, while I try to find topological invariants for a group.

However, it is clear that the functor I defined above is only an example of a functor of $ mathbf {Grp} $ at $ mathbf {Top} $ and (I think) is not going to be very useful.

So my question is,

Is there a useful topological invariant of a group? More specifically, since any group can be associated with a topological space (as we did for the fundamental groups)? If yes, can we talk about literature?