Did you know that one of the strongest remaining core of IBM mainframe users are the large railroad companies? We don't know the complete answer why, but can guess that it has something to do with 24-7-365 operations that can't be put on hold while a platform switch is performed?
Meanwhile, for the employees, access to the mainframes has been crucial since the applications were implemented with scheduling and timecards expected to be entered by all sorts of users. This led the railroads to implement web-based terminal emulation in the early days of the Java Terminal emulators such as Host-On-Demand from IBM and OpenConnect (recently purchased by ActiveOps).
Web downloaded Java applets worked great for easier access to the mainframe--the first access would take a while while the Java objects were downloaded, but subsequent accesses were fairly quick. Until Oracle deprecated the Java Applet, security issues arose, and browsers like Chrome and Firefox became more popular than the original Internet Explorer.
The loss of simple use of Java terminal emulators has hit the Railroad industry hard--those that use OpenConnect have a better option, as there is an HTML emulator for OpenConnect (not great, but it at least works!). Host-on-Demand is another issue, however, as there is no usable HTML version available from IBM to replace it. For our customer, Inventu Viewer+, with pure HTML and Javascript Web Terminal Emulation was the answer.
Today, they have multiple servers (each configured to handle up to 5,000 concurrent sessions) ensuring that their employees have instant access to the mainframe at the click of a mouse.