What are some alternatives?
When comparing Atina and Materia, you can also consider the following products
Flow - Stop managing projects from your inbox.
Moka - Moka is a Gnome Shell theme that uses simple geometry & basic colouring.
Nifty Project Management - Manage projects, work, and communications in one place.
adapta-gtk-theme - An adaptive Gtk+ theme based on Material Design Guidelines - adapta-project/adapta-gtk-theme
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
Zukitwo - Zukitwo is a Gnome Shell and GTK theme that currently works on Gnome Shell 3.14 and the latest version of GTK.