Have a look at fbida. It provides fbi (an image viewer), fbpdf (a PDF viewer), and a few other apps that all run in a framebuffer.

There's also w3m, which is a basic web browser capable of displaying images inline; although this requires some hacking in order to work in a vanilla TTY. What could be easier is a using a kiosk window manager (such as Cage) to launch a lightweight terminal (like st, urxvt, or xterm).

You mean sth like Mutt - mail client for example ?
http://www.mutt.org/#features

You could include pass. It is a password manager that is primarily terminal-based, but because it uses standard GPG encrypted files to do so, they are viewable in your file browser and there are graphical extensions for your web browser.

It also uses Git so you can sync it to a remote repository, and Git can be seen as another application that works in a similar manner. It is terminal-based, but there are graphical front ends like gitg.

Unsure what are those acronyms, but one text-only Linux program I can't recommend enough is ncdu: it helps managing storage in your system, as well as, indirectly, browsing your files.

Pretty much anything using ncurses, no? https://github.com/gabriellluz/awesome_ncurses_apps