awk

A domain-specific language designed for text processing.

hyx

A vim-like hex editor.

sql

Structured Query Language.

visidata

Graphing / data analyses tool.

Text to Diagram

d2

Elegant and easy to use markup + a CLI tool that generates excellent diagrams.

mermaid.js

A client-side JS markup to diagram tool.

graphviz

A swiss army knife graph visualization / diagram tool.

graph-easy

Generate ascii graphs. It's a perl module that uses graphviz as a backend.