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.