A lot of people have already mentioned products I use everyday and almost certainly I stopped checking my email once I started using Slack! Screenhero now bought by Slack has saved me every time I need to collaborate with someone on their machines.
So I'll mention some non obvious ones, Leaf has been a great RSS reader I use since I almost certainly like following individual bloggers /blogs over more notable media channels.
I simply can't put enough praise for HRV4 Training -- I'm an average user, not an athlete but it has really helped me prevent myself from overtraining -- not only does the 2 person developer team post research articles on their latest findings, the duo has been remarkable at taking customer feedback. What's even more amazing is how their gamification is setup -- you simply can't reap the benefits of unlocking features if you're don't measure your heart rate every morning.
I've also use a few free versions but 1password couldn't get more easier for a developer who needs to log in using few logins a few too many times a day.