"Meet Dictation v2.0, a web-based speech recognition app that will transcribe your voice into digital text using the Chrome Speech API. You can also install Dictation as a Chrome App." I tried it and it works pretty well. No special software is needed, so it will run fine on a Chromebook.
Add yourself into your PPT presentation, MS Word, etc. and bring life to your presentations. Free app that runs on the Windows OS and requires a webcam.