Besides Google Chrome and Skype, three come to mind at the moment.
1.) Steam - Absolutely fantastic for all my gaming needs. It's by far the best game distribution software that is available. It has a huge selection of games and the prices are reasonable, and even if you don't have the money to buy them at the moment, Steam often runs amazing sales.
If you don't have it, get Steam here. It's free, but of course, you must purchase the games (Although there are some free ones)
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2.) Paint.NET - Basically just a free alternative to Photoshop, it does all the things I need it to, art wise. The choice in plug-ins makes it a very useful tool for almost any drawing I need to get done. It's the program I use to do things like make my avatars, signatures, animated GIFs, and the like.
It's a reliable program, and if you can't afford Photoshop, this is a good alternative, plus, this hasn't crashed once on me, unlike Photoshop.
If you don't have it, get Paint.NET here. It's completely free, and I highly recommend it, even if you don't plan on using it immediately, it's one of those programs that is good just to have around for when you need it.
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3.) Python (Specifically the GUI IDLE, since it's easier to use than the Command Prompt) - Very simple but useful GUI for Python programming, easier than simply running it through the command prompt. I've found myself spending long nights working on things in Python these days, and this just makes the process a bit faster and easier.
Python is by far my favorite programming language, if you're just getting into programming, Python is a great place to start learning, it has a lot of features that make it one of the best programming languages for beginners and pros alike, at least, in my opinion. Plus, Mac OS and Linux use Python quite a lot.
There are two main versions of Python people use, I personally use Python 3.
If you don't have it, get Python here, it's free, but if you don't know how to program already, it's something you might not find a use for it.