SPFlite
SPFlite is a free file manager and text editor maintained by George Deluca and Robert Hodge. It is similar to IBM's mainframe based ISPF. originally released pre-2012; the current version (as of Mar 26, 2015) is Version 8.2.
It is one of several PC versions of the mainframe ISPF system, some commercial and some freeware versions. See the links for a list.