The O!Play Air O!Link Utility was proprietary which means only Asus had the rights to use it since they're the manufacturers/developers.
However, you can transform a device into something like O!Play using Plex. Plex is a DLNA server that is capable of service music, videos and images through the network. There is support for a very big number of devices and it can be configured extremely easy. Even NAS devices have PLEX modules.
Read more about it using the following link: https://www.plex.tv/