Here are 3 completely free apps that will increase your productivity, keep you on track, and help you achieve more. We utilize these tools on a daily basis internally, we're F'ing sure you'll love them.

Evernote
An awesome app for note-taking and the organization of notes across your devices.
Plan, keep records and manage projects from any device–even offline.
OmniFocus
A personal task manager, the goal is to be able to capture thoughts and ideas into to do lists.
The program uses concepts and techniques described in the book Getting Things Done by David Allen.
Slack
Companies save time with Slack by securely collaborating across teams, departments, offices, and countries. Fewer meetings, less internal email, all your tools integrated into a collaborative app.