MyAssistantOS (My) for Android. It requires a server (backend): https://github.com/mytja/My4Server!
This is a very generic app and ultra simple and light, that was built with MIT AppInventor.
It uses Google Speech Recognition and Your system's default TTS engine (Google, Samsung...)
I hope that I will soonly push a new version, that will come with an open-source code and server changing option.
Currently it gets all the data from server https://my-assistant-eu.herokuapp.com, which comes with a few flaws, which are mentioned in My4Server repository