Simon Dodds, a surgeon in Good Hope Hospital, developed an excellent piece of software to model the flow of patients/service users through a care pathway given constraints of staffing, equipment and facilities. It can be used to determine whether investment in additional resources is warranted and what will happen if you don't - it was sparked when Simon showed the consultants at the hospital that the reduction in length of stay (LOS) they needed was not "lots", but 0.5 day for a LOS of 5 days (much more achievable) to reduce elective surgery cancellations from 70% to less than 30% (cancellations due to no bed being available because of emergencies).
Simon turned this into a book (Three Wins: Service Improvement using value stream design) and a software programme called Care Pathway Simulator which I used for cross-referencing my own computer modelling for redesigning both ECP use across England and urgent care supply in London. It gets a mention here because I get an acknowledgement in the book for the contribution I made in the early stages.
Note Simon Dodds also offers a course in Value stream design and computer simulation (see the www.3-wins.com website)