Yi is described as 'text editor written, and extensible in, the Haskell programming language. It can be made to behave like emacs or like vi' and is an app in the Development category. There are more than 25 alternatives to Yi for a variety of platforms, including Linux, Mac, Windows, BSD and Chrome OS. The best alternative is Visual Studio Code, which is free. Other great apps like Yi are Atom (Free, Open Source), Vim (Free, Open Source), Eclipse (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.
The Kate project develops two main products: KatePart, the advanced editor component which is used in numerous KDE applications requiring a text editing component, and Kate, a MDI text editor application.
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).