UniKey for Windows was first released as a free program in 1999. It quickly gained popularity thanks to its speed, simplicity, and reliability. It soon became, and still is the most popular keyboard program for Vietnamese language. Today, UniKey can be found in almost every Windows PC of Vietnamese people.
The core engine UniKey Vietnamese Input Method is open source and was first released as a part of the x-unikey Vietnamese keyboard for Linux in 2001. Since then, the engine has been integrated in input methods in different OSes and software frameworks. ibus-unikey (developed by Le Quoc Tuan, using UniKey engine) is widely used in Linux distributions.
From Mac OS X Leopard, released in 2007, Apple has integrated UniKey Vietnamese Input Method to the built-in Vietnamese input of Mac OS. From 2010, the engine has also been integrated to the built-in Vietnamese keyboard in iOS (starting from iOS 4.0). So the UniKey engine is now running in all iPhones, iPads that have Vietnamese input.
UniKey is developed by Pham Kim Long. The officical website of UniKey is unikey.org. I’m not responsible for any other sites that offer UniKey software. I don’t recommend downloading UniKey from those websites.