  In this work, we briefly introduce and discuss some of the diversity measures
used in Ecology. After a succinct description and analysis of the most relevant
ones, we single out the Shannon-Weiner index. We justify why it is the most
informative and relevant one for measuring software diversity. Then, we show
how it can be used for effectively assessing the diversity of various real
software ecosystems. We discover in the process a frequently overlooked
software monopoly, and its key security implications. We finally extract some
conclusions from the results obtained, focusing mostly on their security
implications.
