Multi-purpose calculator with customizable functions, units, arbitrary precision, plotting (it includes a GUI).
A powerful, double-entry accounting system from the command-line; it uses a simple yet powerful text syntax to specify the items to account.
The program runs in background, collecting information regarding open windows, focussed ones, etc.; it can be configured to display statistics on the collected data, e.g., figuring out the time spent on one specific window.
Darwin Mail - Inbox evolved: reach new levels of productivity.
Refined Evernote desktop app
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In 2015, I created a course called "How To Eliminate Your Procrastination and DOUBLE Your Productivity.