[adorable]

Does anybody know what the existing open-source / free alternatives are? (that you could run on your own servers)?

[woodson]

The Kaldi toolkit is state of the art, but you have to know quite a bit about speech and natural language processing to create a comparable service that works well (or invest the time to learn it). Definitely not plug and play, though.

Then there are implementations of Baidu’s DeepSpeech (PaddlePaddle: https://github.com/PaddlePaddle/DeepSpeech, or Mozilla’s version).