What is the goal of middleware in distributed system?

Question

What is the goal of middleware in distributed system?

Answer 1

I look at a "distributed" environment meaning many different types of machines with multiple variety of operating systems.

Middleware allows these different operating systems to communicated with eachother.  

For example,  a MAC might have one type of output for an application.  A middleware program will sit between the MAC and say a MS client and translate it as a gateway so that both the MAC and MS Client can use the output!