Smultron is described as 'text editor for Mac OS X Leopard 10.5 which is both easy to use and powerful. It is designed to neither confuse newcomers nor disappoint advanced users' and is a popular app in the Development category. There are more than 50 alternatives to Smultron for a variety of platforms, including Windows, Mac, Linux, BSD and Online / Web-based. The best alternative is Visual Studio Code, which is free. Other great apps like Smultron are Notepad++ (Free, Open Source), Sublime Text (Free Personal), Vim (Free, Open Source) and VSCodium (Free, Open Source).
VS Code is more than just a code editor, it provides the tools and extensions to compile, debug, compare, refactor, and even manage code repositories all within a highly-customised development environment.
Bluefish is a powerful editor targeted towards programmers and webdesigners, with many options to write websites, scripts and programming code. Bluefish supports many programming and markup languages, and it focuses on editing dynamic and interactive websites.
Pinegrow is a Mac, Windows and Linux web editor that lets you build responsive websites faster with live multi-page editing, CSS & SASS styling, CSS Grid editor and smart components for Bootstrap, Foundation and WordPress.
CudaText is a cross-platform text editor, written in Lazarus. It starts quite fast (0.5 sec with ~30 plugins on CPU Intel Core i3 3Hz). It is extensible by Python add-ons (plugins, linters, code tree parsers, external tools).