In one example, a commercial software vendor ships two Python interpreters to power the back end of a commercial user interface. One interpreter is reserved as an application launcher for GPL-licensed code, while the other interpreter runs the non-GPL code, meaning that the two categories of code communicate ''at arms length". In another example, a biotech company has adopted a vertical integration strategy and develops on top of sire computational chemistry software to support internal drug discovery projects. The software is not distributed in a legal sense, and this mode of usage is fully compliant with the GPL license. Where appropriate, code modifications and enhancements are contributed back to the community under the GPL. Cloud-computing businesses that provide software as service offerings through the Internet may provide network access to software derived from sire hosted on a server without having to distribute the source code. One ongoing challenge of the choice of GPL is that it creates an imbalance within the academic community. While sire (and its derivatives) are free to build on academic code released under non-copyleft BSD/MIT-style licenses, those communities are not able to pull code from sire into their codebases without re-licensing to GPL. A part-solution to this is that the sire developers are good community citizens, and are happy to discuss extraction and relicensing of subsets of the Python and C++ code from sire under non-copyleft open source licenses where it is clear that this is to support other open community-driven molecular simulation codes.