I've seen these for at least: - payment processing - mail order sending (retail market) - insurance databases All on fairly large (world-sized) markets. Nev

I've seen these for at least: - payment processing - mail order sending (retail market) - insurance databases All on fairly large (world-sized) markets. Never programmed these myself, but had to interface (file or api) with it. My feeling is that high reliability / data throughput is favored over programmer productivity and data structure elegance (most data I've seen there was fixed width strings :-). See Host Integration Server (http://www.microsoft.com/biztalk/en/us/host-integration.aspx http://www.microsoft.com/biztalk/en/us/host-integration.aspx) for an example of product that allows to use .Net (I guess, even IronRuby) to talk to a mainframe.