The prominent role of software in nanotechnology research and development suggests that open source development methods might offer advantages in improving reliability, performance and accessibility. Open source approaches have shown new opportunities for voluntary cooperation to create and improve complex software. Suitable software licences could be used to promote access, compatibility and sharing of improvements. Many companies currently associated with nanotechnology produce materials, equipment and research and development services, all of which could support open source business models; however, no company yet emphasizes an open source strategy. Some molecular modelling software is already open source or public domain. Software for molecular engineering constitutes an important opportunity for open sourcing, especially if systems architectures encouraging collaboration can be further developed. Analysis suggests that the net impact of open sourcing would be to enhance safety. Initiatives for open sourcing of molecular nanotechnology could be strengthened by coalition building, and appropriate strategies for open source licensing of copyrights and patents.