Ubuntu is the most popular Linux distribution and comes with a great UI. One of the best feature of Linux is the tons of customization options present. However, if you like Mac UI more the there are various themes for Ubuntu which will give you the feel of Mac’s design on Ubuntu.
OS X El Capitan (GTK, Unity & Cinnamon)
This great OS X Theme for Cinnamon and GTK 3.0 Desktops in active development is one of the best. The theme supports GNOME 3.18 and works flawlessly on Ubuntu 15.10. Download it from GNOME-Look.org.
Ubuntu OS X Mavesemite
One of the better Mac like themes for Ubuntu, yet lacking a few tidbits here and there, Ubuntu OS X Mavesemite is a great and aesthetically pleasing theme. Download Ubuntu OS X Mavesemite theme for GTK 3.x.
Zukimac works flawlessly on Unity and GNOME desktop environments which makes it a perfect choice for Ubuntu and Fedora both. While it’s available for GTK 3.10, GTK 3.12 and GTK 3.14, it works great on latest versions also. The Zukimac theme is available for Ubuntu, Fedora, ArchLinux and other distributions.
Mavericks is one of the best themes but works best with the GNOME Desktop Environment, as in Ubuntu GNOME and Fedora. It also works great on Cinnamon as claimed by an ArchLinux user in comments on the download page.
White theme is a simple theme based on the clean design interface of OS X Yosemite and El Capitan on GTK 3.18. Download White 3.18.