Sinhetic is a transliterator app to convert Latin script phonetic Sinhala to Unicode Sinhala. It is based on the UCSC Real Time Unicode Converter and uses the Sinhala Spell Dictionary for OpenOffice.org 3.0 by Buddhika Laknath for dictionary lookup.
Version: 1.0 - Released: 20 April, 2014
Sorry, but you need to have Sinhala installed on your phone for this app to work. I tried unsuccessfully to create a workaround using web fonts, but to no avail.
iOS devices already have Sinhala. If you're on Android, Malinthe has a great guide.
I have a rather shady demo running off my Dropbox
The demo is at janithl.github.io/sinhetic/.
The code has been wrapped in a simple Cordova app and put on Google Play as a free Android app.
Sinhetic is released under the MIT License.