It's FOSS - https://itsfoss.com/use-unity-ubuntu-17-10/
Brief: If you are feeling nostalgic, you can easily install Unity in Ubuntu 17.10. Here’s how to do it.
The most talked about feature of Ubuntu 17.10 is the switch to GNOME. Ubuntu has done quite a good job in making Unity users feel at home with the customized GNOME desktop.
But it is not necessary that you will like GNOME. Unity has been part of Ubuntu for last 6 years and over the time, it did gain its fair share of fan following.
If you are among the ones who have upgraded to Ubuntu 17.10 but want to