LyX (free) - graphical document processing interface using LaTeX
Atom - Customizable text editor by GitHub. Allows for real-time collaboration (!) and has not-too-clumsy Git integration.
Spacemacs - A distribution of Emacs, at the deep end of customizable text editors. Emacs has many "modes"; the most useful is probably Org mode, which is a kind of outliner+agenda that can be used to rapidly create LaTeX/Beamer files, and for literate programming (think Jupyter), among other uses. Compared to plain Emacs, Spacemacs starts with a better configuration that is more modular and easier to customize, and allows for the (optional) use of Vim keybindings.