Not sure about this Brian, but just from looking through the sites of a few programmes this one... XML Copy Editor appears to be one that's been worked on most recently. The latest version 1.2.0.4 came out in April this year...so fairly recent. Some of the others I looked at hadn't been worked on for a few years.
It's available for Windows and Linux. They seem to have binaries for a number of Linux distros...so possibly available in the distro repositories through the package manager software.