https://www.quora.com/What-are-the-top-ten-speech-recognition-APIs

Online short utterance

1) Google Speech API – best speech technology, recently announced to be available for commercial use. Currently in beta status. Google also has separate APIs for Android OS and Javascript API for Chrome.

2) Microsoft Cognitive Services – Bing Speech API same from Microsoft, many different nice addons like voice authentication

3) API.AI – analyses intent, not simply recognizes speech. Useful to build command applications, belongs to Google.

There are also offerings from Amazon, Facebook and many others.

Online large files

4) Speechmatics – large vocabulary transcription in the cloud, US and UK English, high accuracy.

5) Vocapia Speech to Text API – not very user friendly, but a good technology

Offline Proprietary

6) Speech Engine_IFLYTEK CO.,LTD. not very well known Chinese company, but it continuously excels in competitions.

7) UWP Speech recognition from Microsoft for Universal Windows Platform

Open Source

8) CMU Sphinx – Speech Recognition Toolkit – offline speech recognition, due to low resource requirements can be used on mobile. OpenEars – Pocketsphinx on iOS, there are also APIs for Node.js, Ruby, Java, Android bindings.

9) Kaldi – speech recognition toolkit for research. UFAL-DSG/cloud-asr – Kaldi-based cloud platform, alumae/kaldi-gstreamer-server – another kaldi-based cloud platform. iOS Speech Recognition – kaldi adopted for offline recognition on iOS from Keen Research.