The Half-life of Software
The half-life of Software is the time required for a half of Software developed today to disappear from the market. Today the Half-life of Software is 4 years. The number I found analyzing the lifetime of 200+ discontinued Software.
There is an intriguing connection to Kruchten's hypothesis about five-year half-time of software engineering ideas, concepts, tools, and methods.
An IBM study indicates that application programs, on average, have a very short life (14 months).