The number of software systems is increasing at a rapid rate. For example, SourceForge currently has about sixty thousand software systems registered, twenty-two thousand of which were added in the past twelve months. It is important for software evolution to search and use existing similar software systems from software archive. An evolution history of an existing similar software system is useful. We may even evolve a software system based on an existing one instead of creating it from scratch. In this paper, we propose automatic software categorization algorithm to help finding similar software systems in software archive. At present, we leave open the issue about the nature of the categorization, and explore several known approaches including code clones-based similarity metric, decision trees, and latent semantic analysis. The results from applying each of the approaches gives us some insights into the problem space, and sets some directions for further work.