Sunt câțiva jucători importanți cu care m-am uitat sau am lucrat:
Voxeo: Early versions used the Nuance ASR but I believe they use their own now. Uses VoiceXML and CCXML for call control. They get expensive as you scale up but the development license (2 ports) is free.
Loquendo: I only list this because a) I did demo it and b) they have the best TTS engine I've ever heard. Seriously worth a demo just to hear the quality.
Nuance Voice Platform (NVP): I work with this almost daily. Nuance has by far the most powerful ASR on the market but it comes at a big price. If you have to ask about price then don't bother falling in love with the quality of the engine. It uses a somewhat tweaked version of VoiceXML.
Microsoft Speech Server: You already know this one of course. Bang for the buck it is a wonderful platform. The VoiceXML support is borderline (limited control over the engine from VXML properties) but if you're willing to use Workflows instead you can do just about anything you want. The ASR is good although it doesn't have near the accuracy with large or complex grammars like Nuance. This is currently my preferred platform for most applications. And like Voxeo the Developer license is free.