Atom has a built-in package manager and an extensive [list of packages](https://atom.io/packages). Packages are written in CoffeeScript.
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Pro Fast and smart contextual assistance
Uses a fast indexing technique to provide contextual hints (auto-completion, available object members, import suggestions).
On-the-fly code analysis to detect errors and propose refactorization.
Pro Smart refactorings
IDEA places an emphasis in safe refactoring, offering a variety of features to make this possible for a variety of languages.
These features include safe delete, type migration and replacing method code duplicates.
Pro Lots of plugins
Many plugins are available for almost any task a developer may need to cover. Plugins are developed by Jetbrains themselves or by 3rd parties through the SDK available for writing them.
Pro Android support, JavaEE support, etc
A very complete development environment support.
Pro Stable and robust
IntelliJ IDEA hardly ever crashes or has any issues that plague other Java IDEs like file corruption or slowness.
Pro Intuitive and slick UI
IDEA has a clean, intuitive interface with some customization available (such as the Darcula theme).
Pro Support for many languages
IntelliJ supports many languages besides Java, some of these are: golang, Scala, Clojure, Groovy, Bash, etc...
Pro Free version available
There is a free community edition (open source) and an ultimate edition, which you can compare here.
The ultimate edition is available for free for one year for students but must be registered through an .edu e-mail account.
Pro Clear and detailed documentation
The documentation is exhaustive, easy to navigate, and clearly worded.
Pro Very powerful debugger
With ability to step into a certain part of a large method invocation (Shift+F7), drop frame, executing code snippets, showing method return values, etc.
Pro Many convenient features
These simplify the daily work, e.g. copy/cut a whole line without the need to select it.
Pro Extensive list of packages
Atom has a built-in package manager and an extensive list of packages. Packages are written in CoffeeScript.
Pro Built-in package management
Atom was built from the ground up with the community in mind. Package management is therefore a first class feature.
Due to its modular design, almost any aspect of the editor can be changed. Even seemingly core packages, like those taking care of search and replace functionality, can be forked on GitHub, and changed and replaced in the editor.
The documentation for creating new plugins is also great, making it easier for developers to jump in and create plugins for Atom.
Atom can run on Mac, Windows, and Linux.
Pro Free and open source
Atom is free, open source, and written in C++, LESS, and CoffeeScript.
Pro Beginner friendly
One of the goals of Atom is to be a text editor for both experienced and beginner programmers. You can add keyboard shortcuts, change themes, install plugins, and change core settings by clicking through a GUI, or by manually editing config files the old-fashioned way. It has the added advantage of being built using the same engine that powers Google Chrome, so actions like opening and closing tabs feel familiar, even to new or non-programmers.
Pro Embedded Git control
Atom will highlight folders, files, and lines that have any uncommitted edits made. It also integrates really well with GitHub.
Pro Multi-line select and edit
Multiple cursors and column selection allow for versatile ways of editing.
ctrl + d will select the current word and each time the command is repeated, it adds the next occurrence of the word to the selection.
ctrl + click or
middle-mouse click will place another cursor in the place that's clicked. Cursors can then be controlled together. This also allows for selecting vertically.
Pro Command Palette support
The Command Palette permits fuzzy searching all available functions, settings, snippets, etc.
Pro Allows for instant file switching
By pressing Ctrl or Command + T and using fuzzy search, you can look for a file in your project.
Pro Command line integration out of the box
Installing Atom adds two command line commands -
apm. The first one runs the application itself while the second is the Atom Package Manager that's used to add and remove various components from the package listing. While these features can be set up with other editors as well, Atom takes care of them out of the box.
Pro HiDPI support
Atom has built-in HiDPI support with zero scaling issues.
You can theme and customize Atom to your liking.
Pro Vim plugin turns Atom into a modernized vim
Pro Modern feel and very customizable and extendable
Pro Best support for Arduino with Platformio
Arduino is the most important platform for developing embedded systems.
Con Built with closed source components
The version with full features is not opensource. Parts of the code are under apache licence though.
Con Bugs are not solved as often as they should
They are more interested in adding new features or issuing new versions than solving bugs.
Con Slow startup
Con Uses too much RAM
Con Cannot open multiple projects in the same window
Con Lack of plugins
IntelliJ supports a very small amount of plugins. Althrough thesse are 'quality approved', many features are missing and can't be implemented because of that.
Con Standard hotkeys behave differently
Seems like hotkeys assignment in Idea has no logical consistency.
Like «F3» is usually next match, «Ctrl+W» - close tab, etc — they map to some different action by default.
There is a good effort in making the IDE friendly for immigrants from other products: there are options to use hotkeys from Eclipse, and even emacs. But these mappings are very incomplete. And help pages do not take this remapping into account, rather mentioning the standard hotkeys.
So, people coming from other IDEs/editors are doomed to using mouse and context menus (which are rather big and complex).
Con Very slow startup time
Atom is very slow to startup, which is a big disadvantage if you are accustomed to using it to make quick changes on your files.
Con High memory usage
Atom has a relatively high memory usage, especially when compared to some other text editors not based on Electron. For those who develop on the go, this also tends to mean shorter battery life.
Con Has difficulty with large text files
Tends to crash or hang with large >(10MB) text files, making it less useful as a general text editor.
Con Slows down exponentially with plugins
Extending it needs sacrificing responsiveness
Con No text UI
Con Doesn't handle RTL (right-to-left text) well
Text can't be highlighted and manipulated properly, cursor isn't displayed visually according to where it is logically (you have to type to find out), and similar issues.
Con Not known when a new window will open
It's not really clear why and when a new window is opened when you open a file out of the tree view.
Con Depends on old software
Depends on python 2, which dies out.
Atom is not a native application. As such performance is subpar and the lag is especially noticeable on larger projects. It also opens a surprising amount of sub-processes and leaks a considerable amount of memory.
Con Missing additional touches
As Atom is still relatively new, it's missing nice little touches that other text editors have implemented over the years. From simple ease-of-use items like middle-mouse button multi-cursor select, to the ways pasted information from a spreadsheet is interpreted in multi-select situations.
Con Doesn't recognize some keyboards
Con Crash and data loss
I lost unsaved changes 2 times when the app crashes.
A bugreport about that was closed automatically after some time, nobody cares.