TUI is an AmiBlitz-specific GUI toolkit that uses specially written libraries to generate the interface. The interface is somewhat similar to MUI in use, but it doesn't require the installation of a 3rd party toolkit to use it.
Two variants are available: The original TUI and a new version called NTUI. Both are implemented as includes instead of Blitz libraries, so to use them you need to XInclude tui.include.ab3 or ntui.include.ab3 as required. TUI is older and had been used successfully in a number of large and small projects, whereas NTUI is less established; however, NTUI offers a more modern approach with more flexibility, using XML files to define the interface elements.