Window 10 has a free word prediction feature that works anywhere you are typing within Windows 10!  Check it out:

How to turn on Windows 10 word prediction|
Using Word Prediction for Inclusive Classrooms
VIDEO:  You can turn on text suggestions in Windows 10

Co:Writer Universal is a chrome extension and an app.

What is Co:Writer Universal?
Co:Writer Universal iOS App
Co:Writer Universal Chrome Extension
VIDEO: How to use Word Prediction in Co:Writer

Word Q 5 is desktop software and iWordQ is an app.

Word Q  features
VIDEO: Word Q Software Overview
VIDEO: SETC Webinar: Empowering Writers with Word Q 5 Support

Read&Write a desktop software, chrome extension and iPad app.

Read&Write Free for Teachers
VIDEO: Using Prediction in Read&Write for Google Chrome
Read&Write for iPad