Many open source software projects are not very open to third party developers. The point of open source is to enable anyone to fix bugs or add desired capabilities without holding them hostage to the original developers. This principle is important because an open source project's developers may be unresponsive or unable to meet third party needs, even if funding support for requested improvements is offered.This paper presents a simple rating system for evaluating the openness of software distributions. The rating system considers factors such as platform portability, documentation, licensing, and contribution policy. Several popular open source products are rated in order to illustrate the efficacy of the rating system.