We could not have foreseen, in 2005, that nearly 20 years later sire would still be being developed and in use by industrial and academic groups internationally. Creating software that is deliberately meant to be hidden and not visible to end-user researchers has many challenges. The software has been executed millions of times , but often with most researchers being oblivious to that use. And so arguing for and financing its continued maintenance and development is difficult, as it is not immediately obvious why sire is important, or what it does. Conversely, a delicate balance is always walked between making sire more visible and more capable as a foundation for other programs, while also not going so far as to replace or compete with the other packages in the rich biomolecular simulation software ecosystem on which we depend. But, as academic software development moves away from self-contained codes, and developers move more towards a "divide and conquer" approach of providing small, well-defined software solutions, we have learned exactly what sire is and how we achieve that balance. Sire is a molecular information and interoperability engine, which makes it easier to combine and leverage the functionality of many other programs and libraries. It is the interoperability layer that provides a "town square" where other programs can meet and exchange molecular information and functionality. Keeping that in mind, and being good citizens in the wider community of open source biomolecular simulation software developers, should help ensure that the use of sire grows and that it continues to be actively developed, maintained and useful for academic and industrial researchers for many years to come. industrial-academic partnerships funded via EPSRC Impact Acceleration Accounts (University of Bristol 2016, and University of Edinburgh, IAAPIII074) and InnovateUK funding (KTP partnership 011120); industrial partners and other supporting organisations on many of these awards, from Cresset, Drug Design Data Resource, Evotec, Exscientia, Memorial Sloan-Kettering Cancer Centre, Molecular Science Software Institute, Software Sustainability Institute, Syngenta, and UCB; EPSRC research fellowships awarded to CJW (EP/N018591/1) and AM (EP/G007705/1) and Royal Society University Research Fellowship and ERC Starting Grant (336289) awarded to JM. We also acknowledge the support of the wider simulation community, particular CCPBioSim (EP/J010588/1, EP/T026308/1) for helping organise and host training workshops for sire-derived codes, and supporting funding applications for its continued development. We acknowledge support fron HECBioSim (EP/R029407/1, EP/R029407/2, EP/X035603/1) for provision of high-performance computing resources to validate scientific methodologies implemented by sire-derived codes.