One Thing 1.11.2 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free software for Mac OS X is a product of Veenix, LLC. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The software is included in Design & Photo Tools.
From the developer:
One Thing is a quick and easy-to-use app that helps us focus on and get things done "one thing" at a time. You just need to click on the disclosure triangle to expand the window or select "Expand Window" from the "File" menu, enter your text, choose a text color by clicking on the Color Button, and click on the disclosure triangle to close the window.
You may want to check out more Mac applications, such as Thinkin' Things 1, The Next BIG Thing or Things, which might be similar to One Thing.