I agree with Matt that CATT is good. Reasonably featured, reasonably priced.
I have no experience with t27 eXpress, but it's been around for a while.
I have been using InfoConnect for years. Attachmate is now part of
MicroFocus.
https://www.microfocus.com/products/infoconnect/unisys/.
I believe that some versions of Attachmate Reflection (also now in
MicroFocus) also support MCP systems. These are enterprise-class
products -- fully-featured, with pricing to match.
There is a Java-based emulator, WebEnabler, that is bundled with the
MCP. It's basic, but works fine. It does not connect over Telnet, but
goes in over a plain TCP/IP port through CCF to COMS. I think most of
the other emulators also now support that pathway.
Core Technology used to be a significant player in MCP terminal
emulation, but I don't hear about them anymore. From their web site,
though, they still market at least a Java-based version of CTCBridge:
http://coretechcorp.com/terminal-emulation/.
--
Paul