I have been searching for a software-based Miracast solution for quite some time. iOS and AirPlay have had Reflector, AirServer, and more, but mirroring from Android or Windows has required a hardware Miracast receiver.
This past summer Microsoft released updates to Windows 8.1 with some promising comments about using Windows as a Miracast receiver. The updates enabled the capability, but didn't add the actual receiver; that was up to developers and needed updated hardware drivers.
Then at the end of October AirServer announced AirServer Universal, a new version adding Miracast to their existing AirPlay receiver software. There are some specific requirements to get it working. Unfortunately for Mac users, this only works with Windows 8.1. Your computer must also have a network device with a new NDIS 6.40 device driver. If you don't have a supported network chip, you can simply add the Asus USB-AC56 adapter. The combined price of the adapter and AirServer is under $100. I also installed AirServer on a sub-$400 Acer Switch 10 convertible laptop and was satisfied with the performance, even with two iPads (2nd generation) connected along with a Nexus 5. The Switch 10 did not require the Asus adapter.
AirServer has worked well as a Miracast receiver with every device I have tried, including a Nexus 5, Nexus 7 (2013), Nvidia Tegra Note 7, and Acer Switch 10 Windows 8 convertible laptop. Miracast connections from the Nexus devices did take longer to establish than other devices, and initially appeared to have significant input lag, but it improves fairly quickly. I created a video showing the Nexus 5 used alongside an iPad 3, connecting with a Nexus 7, and a game. The audio in the game is choppy, but that has been true with every Miracast receiver I have used. One interesting discovery is that I had to use the Asus USB-AC56 to get the Miracast capability of AirServer installed, but then was able to just use my laptop's existing wireless chip. I removed the Asus adapter completely and was still able to connect from the Nexus 5, Tegra Note, and Acer Switch. The Nexus 7 still saw AirServer as a receiver but it wouldn't connect unless I used the Asus adapter.
In addition to the system requirements, there are other limitations. AirServer only supports one Miracast device at a time. You can still have multiple iOS devices along with that single Miracast device. AirServer says support for multiple Miracast devices is coming. The other limitation is actually a Miracast issue more than a problem with AirServer. A device sending a Miracast signal will always send a landscape image. If your screen is in portrait mode, the device will rotate it and convert it to landscape before sending it to AirServer. If that is the only device being mirrored, it's not a problem. It is a problem when sharing the screen with an iOS device. In those situations the Miracast screen appears smaller than the iOS screen (as seen in the video linked above). AirServer may implement a workaround in a future update but isn't making any promises.
While not perfect, Airserver Universal is a step in the right direction for enabling a true BYOD environment.