Previously the app was only available preloaded on Alexa is now available from the Windows 10 store., but
The Wake on Voice feature is still only available on "supported devices" but users can set up keyboard shortcuts or click on the Alexa button within the app. Unusually, the minimum specs include just a mouse and keyboard, but an Amazon spokesperson has confirmed a microphone is also required.
While there is one review on the app reporting that this version of Alexa can't install skills or access smart home features, the Amazon representative says that you can control devices if you set them up with the web app first.
The new app is part of an attempt to get PCs and Alexa to work better together. In August, Microsoft announced that it's now possible to, a feature which works with the Xbox One game console.
Updated 1.51 p.m. ET: Now includes comments from Amazon