Pandoc is a Haskell library for converting from one markup format to another, and a command-line tool that uses this library.
Cost / License
- Free
- Open Source (GPL-2.0)
Platforms
- Mac
- Windows
- Linux

txt2tags is described as 'It reads a text file with minimal markup such as bold and //italic// and converts it to the following formats (among others):' and is a Code Editor in the development category. There are eight alternatives to txt2tags for a variety of platforms, including Linux, Mac, Windows, Web-based and Self-Hosted apps. The best txt2tags alternative is Pandoc, which is both free and Open Source. Other great apps like txt2tags are Textile, Asciidoctor, AsciiDoc and PHP Markdown.
Pandoc is a Haskell library for converting from one markup format to another, and a command-line tool that uses this library.

Textile is a lightweight markup language originally developed by Dean Allen and billed as a "humane web text generator". Textile converts its marked-up text input to valid, well-formed XHTML and also inserts character entity references for apostrophes, opening and...
Asciidoctor is a fast text processor and publishing toolchain for converting AsciiDoc content to HTML5, DocBook 5 (or 4.5) and other formats.

Text processor for AsciiDoc format https://en.wikipedia.org/wiki/AsciiDoc which is human readable text format, similar to Markdown format, but with more complex syntax usage (but not so complex like LaTeX).

Docutils is an open-source text processing system for processing plaintext documentation into useful formats, such as HTML, LaTeX, man-pages, open-document or XML. It includes reStructuredText, the easy to read, easy to use, what-you-see-is-what-you-get plaintext markup language.

The MarkItDown library is a utility tool for converting various files to Markdown (e.g., for indexing, text analysis, etc.).