Large graphs are used in many applications, such as social networking. The management of these graphs poses new challenges because such graphs are too large to fit on a single server. Current distributed techniques such as map-reduce and Pregel are not well-suited for processing interactive adhoc queries against large graphs. In this paper we demonstrate Horton, a distributed interactive query execution engine for large graphs. Horton defines a query language that allows expressing regular language reachability queries and provides a query execution engine with a query optimizer that allows interactive execution of queries on large distributed graphs in parallel. In the demo, we show the functionality of Horton managing a large graph for a social networking application called Codebook, in which a graph models data on software components, developers, development artifacts (such as bug reports), and their interactions in large software projects.