Is it possible to have two sources of audio output to different speakers in Windows 10?

I found two applications that allows you to do this.

CheVolume (Paid) - 7 day trial version available

Audio Router (Free) - open source alternative to CheVolume

Note: If not working you need to enable stereo mix in sound properties. Refer this video or this GIF.

Update after spring 2018

With windows 10 spring update 2018, Microsoft is offering a similar solution. You can check the below GIF or this youtube video.

Update December 2018

EarTrumpet - Quick, simple control of all your audio devices from the taskbar. Get it here.

Supported operating systems

• Windows 10 1803 (April 2018 Update)
• Windows 10 1809 (October 2018 Update)

Though Codelt already answered the question, it should be known that the terrific Pulse Audio has builds available for Windows:

• PulseAudio on Windows
• Setting up PulseAudio 1.0 beta for Windows

Pulse Audio has been providing this feature on Linux desktops for about four or five years, therefore it is stable and reliable. Additionally, it is very scriptable so the user can have it automatically route based on conditions after some configuration. So far as I know neither of the mentioned Windows-only software are scriptable.

You can now do this in later builds of Windows 10.
I don't know on which build it started.
Go to Settings --> Sound.
At the bottom, there's Other sound options --> App volume and device preferences.