Kõnele is an Android app that offers speech-to-text user interfaces to other apps. Its main components are:

a voice search panel (i.e. a RecognizerIntent activity)
a speech keyboard that implements the input method editor (IME) API
two implementations of SpeechRecognizer, backed by two open source speech recognition servers
https://github.com/alumae/kaldi-gstreamer-server
(not maintained) https://github.com/alumae/ruby-pocketsphinx-server