- GNU poke - an interactive, extensible editor for binary data. Not limited to editing basic entities such as bits and bytes, it provides a full-fledged procedural, interactive programming language designed to describe data structures and to operate on them. 
- Kaitai Struct - A new way to develop parsers for binary structures, a declarative binary format parsing language
- https://github.com/binspector/binspector - A binary format analysis tool
- https://github.com/igitur/ffe - Flat File Extractor
- Veles - Binary Analysis Tool - CodiSec CodiSec - New open source tool for binary data analysis
- https://en.wikipedia.org/wiki/Text_editor - a type of computer program that edits plain text. Such programs are sometimes known as "notepad" software, following the naming of Microsoft Notepad. Text editors are provided with operating systems and software development packages, and can be used to change files such as configuration files, documentation files and programming language source code.
- https://en.wikipedia.org/wiki/TECO_(text_editor) - Text Editor & COrrector is both a character-oriented text editor and a programming language, that was developed in 1962 for use on Digital Equipment Corporation computers, and has since become available on PCs and Unix. Dan Murphy developed TECO while a student at the Massachusetts Institute of Technology (MIT).
According to Murphy, the initial acronym was "Tape Editor and Corrector" because "punched paper tape was the only medium for the storage of program source on our PDP-1. There was no hard disk, floppy disk, magnetic tape (magtape), or network." By the time TECO was made available for general use, the name had become "Text Editor and Corrector," since even the PDP-1 version by then supported other media. It was subsequently modified by many other people and is a direct ancestor of Emacs, which was originally implemented in TECO macros.
- https://en.wikipedia.org/wiki/QED_(text_editor) - a line-oriented computer text editor that was developed by Butler Lampson and L. Peter Deutsch for the Berkeley Timesharing System running on the SDS 940. It was implemented by L. Peter Deutsch and Dana Angluin between 1965 and 1966. QED (for "quick editor") addressed teleprinter usage, but systems "for CRT displays [were] not considered, since many of their design considerations [were] quite different."
- https://en.wikipedia.org/wiki/Ed_(text_editor) - a line editor for the Unix operating system. It was one of the first parts of the Unix operating system that was developed, in August 1969. It remains part of the POSIX and Open Group standards for Unix-based operating systems, alongside the more sophisticated full-screen editor vi.
- https://sourceforge.net/p/joe-editor - Joe is world-famous Wordstar like text editor.
- sandy - a (suckless) ncurses text editor with an easy-to-read, hackable C source. Sandy tries to maximize screen estate, minimize the SLOC used and not get in your way too much. It can somehow be controlled using a named pipe that lives in /tmp and all preferences and keybindings are to be chosen at compile time.
- Kakoune - Modal editor. Faster as in less keystrokes. Multiple selections. Orthogonal design.
- https://github.com/jdugan6240/powerline.kak - Powerline plugin for Kakoune Editor.
- dred - built from the ground up as a fast, ultra lightweight alternative to other modern text editors. It does away with that annoying trend of loading an entire web browser in the background and instead focuses on just getting out of the way and letting you get on with it.
- ne - the nice editor, a free (GPL'd) text editor based on the POSIX standard that runs (we hope) on almost any UN*X machine. ne is easy to use for the beginner, but powerful and fully configurable for the wizard, and most sparing in its resource usage. If you have the resources and the patience to use emacs or the right mental twist to use vi then probably ne is not for you.
- https://github.com/antirez/kilo - A text editor in less than 1000 LOC with syntax highlight and search.
- https://github.com/udo-munk/s - A tiny vi like screen editor
- https://github.com/evanmiller/hecate - 🔥 The Hex Editor From Hell! 🔥 - a terminal hex editor unlike any you've ever seen: instead of putting the (ASCII) representation of bytes way out on the right side of the screen, it puts the interpreted values directly beneath the hex representation. If that weren't exciting enough, you can move the cursor around using Vim-like controls and interpret the underlying bytes as an integer, float, etc. -- perfect for your reverse-engineering needs.But wait, there's more! Hecate (pronounced HECK-it, named after the Greek goddess of witchcraft) features tabbed browsing, in-place editing, large-file support, full-file searching, and arbitrary expressions for specifying an offset within a file.
- https://github.com/solemnwarning/rehex - A cross-platform (Windows, Linux, Mac) hex editor for reverse engineering, and everything else. 
- wxHexEditor - a Free Hex Editor / Disk Editor for Huge Files or Devices on Linux, Windows and MacOSX
- 010 Editor - Pro Text/Hex Editor | Edit 160+ Formats | Fast & Powerful - $$
- https://github.com/tsujan/FeatherPad - Lightweight Qt5 Plain-Text Editor for Linux
- https://foicica.com/textadept/ Textadept is a fast, minimalist, and remarkably extensible cross-platform text editor.
- WordGrinder is a Unicode-aware character cell word processor that runs in a terminal (or a Windows console). It is designed to get the hell out of your way and let you get some work done.It's designed for writing text. It gets out of your way and lets you type.
- Oni - Mouse-free productivity with the perks of modern code editors. Open-source, cross-platform, and easy to learn.
- https://github.com/olivierkes/manuskript - an open-source tool for writers. Manuskript runs on on GNU/Linux, Mac OS X, and Windows. Manuskript provides a rich environment to help writers create their first draft and then further refine and edit their masterpiece.
- Ted - an easy rich text processor
- https://github.com/fabiospampinato/notable - The markdown-based note-taking app that doesn't suck. 
- Boostnote - Note-taking app for programmers. Apps available for Mac, Windows, Linux, Android, and iOS. Built with Electron, React + Redux, Webpack, and CSSModules.