TEI XML is a plain text format which can be edited by most code editors. Oxygen XML Editor, which many campuses license (including Notre Dame), has built-in support for XML and TEI validation, and it can perform functions like XSL transformations, which enable editors to convert XML into HTML, plain text, PDF, and so on. The downside is that Oxygen is a commercial product, and can be pricey if you don't have institutional support (check for academic versions).
|Oxygen XML||recommended||A popular application for editing TEI, with support for transforming it into other formats like html.|
|Visual Studio Code||FREE||Powerful, free, and open-source cross-platform editor with support for a range of languages.|
|Notepad++||FREE||A popular and powerful free text editor for Windows, with syntax highlighting for XML and other formats.|
|Atom.io||FREE||Powerful, free, and open-source cross-platform editor with support for a range of languages.|