Text Editors & IDE of choice for everyday usage

Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.

HackMD is a browser-based, real-time collaborative markdown editor. It was inspired by hackpad but focuses more on speed and flexibility.
Features:
Collaboration
PDF, Image, and Video Embedding
Auto-Save and Revision History
Markdown Extensions (TeX, Flowcharts, Emoji, Graphviz, ...)
Book Mode
Presentation Mode (with Themes and Animations)
Easy (Shared) Notetaking via Book Mode
Disqus Integration
and more

Vim ("Vi IMproved") is an advanced text editor that allows syntax highlighting, word completion and has a huge amount of contributed content. It also has a GUI version called GVim.

Code combines the streamlined UI of a modern editor with rich code assistance and navigation, and an integrated debugging experience – without the need for a full IDE.

IntelliJ IDEA is a free / commercial Java IDE by JetBrains. Its design is centered on programmer productivity. A number of its features are intended to accelerate development and allow programmers to concentrate on functionality while IntelliJ IDEA handles routine coding tasks.

IntelliJ IDEA is available in two editions: Ultimate (paid) and Community (free and opensource).

IDEA supports various programming languages with advanced code inspection and refactoring features, such as Groovy, Javascript, Actionscript, Ruby/JRuby, PHP and others.
The Community Edition is Open Source but misses most features for server-side and web development.