Atom plugin for txt2tags
There is also lots of snippets to make your editing easier. Just press b\<tab> for bold, link\<tab> to insert a link or even table\<tab> to insert a table skeleton.
After installing the plugin, go to its Settings screen to get a list of all the available snippets. As an alternative, press Option-Shift-S (or Alt-Shift-S in Windows) while editing a .t2t file to get the same listing.
To install the plugin (aka package, in Atom terms), use the default Atom installer under Settings > Install and search for txt2tags. You can get more information about the plugin at https://atom.io/packages/language-txt2tags.