QXmlEdit is a simple XML editor based on Qt libraries. Its main features are unusual data visualization modes, nice XML manipulation and presentation and it is multi platform. It can split very big XML files into fragments, and compare XML and XSD files. It was born on Google code (https://code.google.com/p/qxmledit).
Latest release is 0.9.13 tagged on May 2019.
Downloads are hosted on sourceforge.net: https://sourceforge.net/projects/qxmledit/files.
Source code packages and binary installers for MacOS and Windows are available.
Chances are that you can find QXmlEdit already packaged in your Linux distribution.
Information about license, source code, support and mailing list in the info page.
Qt libraries version 4.8 or higher are required. Qt 5 is supported.