Download of Virtio-Net 0.9.4 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application lies within System Tools, more precisely Virtualization. The actual developer of this free Mac application is Phil Jordan. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
Virtio-Net is a Mac OS X driver for a Virtio network device. The application is designed to help your Mac interact with Virtio Ethernet devices. Virtio is a fast network device supported by KVM and VirtualBox and allows kernel debugging of guests via GDB.
You may want to check out more Mac applications, such as roami, Transterpreter or Curl, which might be similar to Virtio-Net.