Certain free products of graph operator algebras

We develop a notion of a generalized Cuntz–Krieger family of projections and partial isometries where the range of the partial isometries need not have trivial intersection. We associate to these generalized Cuntz–Krieger families a directed graph, with a coloring function on the edge set. We call such a directed graph an edge-colored directed graph. We then study the C ∗ -algebras and the non-selfadjoint operator algebras associated to edge-colored directed graphs. These algebras arise as free products of directed graph algebras with amalgamation. We then determine the C ∗ -envelopes for a large class of the non-selfadjoint algebras. Finally, we relate properties of the edge-colored directed graphs to properties of the associated C ∗ -algebra, including simplicity and nuclearity. Using the free product description of these algebras we investigate the K-theory of these algebras.