I would try Atom, it's an open source easy to use and powerful text editor. It meets each of your requirements of,
It also has other great features like,
- Built-in package manager - Search for and install new packages or start creating your own—all from within Atom.
- Smart autocompletion - Atom helps you write code faster with a smart, flexible autocomplete.
- File system browser - Easily browse and open a single file, a whole project, or multiple projects in one window.
- Multiple panes - Split your Atom interface into multiple panes to compare and edit code across files.
- Find and replace - Find, preview, and replace text as you type in a file or across all your projects.
- LOTS of packages
- LOTS of themes
- Easy to custimize
- Runs on Electron
- Completely open source
Atom.io
A hackable text editor for the 21st Century.
At GitHub, we're building the text editor we've always wanted. A tool you can customize to do anything, but also use productively on the first day without ever touching a config file. Atom is modern, approachable, and hackable to the core. We can't wait to see what you build with it.