Virtlab simulations were written using Adobe Flash. Flash is no longer supported by Internet vendors, and so Virtlab has closed. You may still be able to find copies of the out of print "Dynamic Models ..." books on which Virtlab was based (e.g., Amazon.com). These books are exercise books that use electronic spreadsheets to simulate the process being explored. You are free to copy whatever you need for yourself or your students. If you have questions please contact me at dbarkley@nsimonco.com.