Editors

Many common text editors can be used to edit TorqueScript files. Some favourites include Sublime Text, Notepad++, Programmer's nodepad, and good old Notepad, Gedit, or TextEdit.
Many editors also support cscope and cscope works with TorqueScript. So you can use cscope for jumping around in the code.

Vim

You can use these plugins to get proper TorqueScript and TAML XML syntax highlighting in vim. Note that this extension will override C# syntax highlighting due to TS's use of the .cs extension.

Notepad++

You can use this plugin to get proper TorqueScript syntax highlighting in Notepad++. Note that this extension will override C# syntax highlighting due to TS's use of the .cs extension.

EMACS

A guide on how prepare EMACS to edit TorqueScript files.
http://forums.torque3d.org/viewtopic.php?f=12&t=173&p=1483&hilit=emacs#p1483

Atom

Adds syntax highlighting and snippets to TorqueScript files in Atom.

https://github.com/portify/language-torquescript

IDEs

Integrated Development Environments let you do more than just edit TorqueScript files - they provide additional features to boost your productivity, such as code browsing and searching, debugging, and syntax checking.

TorqueDev

A fully featured IDE for TorqueScript projects. Formerly known as CodeWeaver.

Now TorqueDev is free GPL license, you can download the source: TorqueDev Source code

TorqueSense

A community-developed plugin for IntelliJ IDEA.

Torsion

A commercial IDE (USD$40) for Torque. Fully featured. Now Torsion is free MIT license, you can download the source: Torsion Source code

TIDE

Cross-platform plugin for jEdit with IDE features like debugging and function browsing.

Debugger for TorqueScript

The GTDB debugger is free/libre software. It works (2017) and you can get it from here.