Just bought my first Macbook, so what free apps should I be downloading?

After a lifetime of Windows, and dabbling in both Ubuntu and Chrome OS, I've made the jump to a Macbook Pro. I've had an iPad and iPod touch in the past, but this is my first time on Apple's desktop OS.

So my question is, which apps should I be downloading? Due to spending all my money on this as an impulse buy, I can only afford free ones. I've downloaded Spotify, Twitter and Chrome, but the rest are up for grabs.

Thanks in advance :)