Ace is a JavaScript-based code editor used by platforms like Cloud9 IDE and GitHub for file editing, offering users features such as indentation with TAB and Shift+TAB, and line commenting with keyboard shortcuts. It supports editing across different browsers, including Safari, Chrome, and Firefox, and provides options to customize tab or space usage and indentation levels. For files in Markdown, Textile, or other rich text formats, GitHub presents a rendered preview instead of a diff. Users can enhance language support by adding new modes via Ace's wiki page, and there is an open invitation to contribute to the editor's development by improving Ace on GitHub. Feedback and suggestions are welcomed, emphasizing the collaborative spirit of the platform.