gedit

gedit is a text editor based on the GTK graphical toolkit.

The first goal of gedit is to be easy to use, with a simple interface by default. More advanced features are available by enabling plugins.

Notable Features

Files are opened in tabs
Full support for internationalized text (UTF-8)
Syntax highlighting for lots of languages (Python, Shell, C, C++, HTML, CSS, JavaScript, XML, Markdown and many others)
Configurable fonts and colors
Print and print preview support
Search and replace with support of regular expressions
A side panel with an integrated file browser
Spell-checking
Word auto-completion
Undo/Redo
Auto indentation
Text wrapping
Line numbers
Right margin
Highlight current line
Highlight matching brackets
Editing files from remote locations
Backup files
A flexible plugin system which can be used to dynamically add new advanced features
List of plugins distributed with gedit

You can install the gedit and gedit-plugins packages.

macOS packages (a bit outdated)
A Homebrew formula for the latest version of gedit is available: brew install gedit

The current way to install gedit on Microsoft Windows is with MSYS2.