I am currently building a visual app for note taking and browsing.
This works on a hierarchy of note files, supported by an SQlite database for searching and arbitrary relationships. I use it on a small (5'', 320x240) display, connected to a Raspberry Pi 400, cyberdeck-style. The UI, implemented with PicoTUI, runs in a terminal window and can be operated by keyboard alone.
Decker-alike in this setup could mean that note files would be individual slides or whole decks of slides. A render engine would display a slide full screen in a terminal window, using only ANSI terminal characters for both widgets and even low-res images. Decker & Lil would provide widgets and scripting, similar what TurboVision & TurboPascal did back in the 90th.