What are some alternatives?
When comparing Iris and Flow, you can also consider the following products
Moka - Moka is a Gnome Shell theme that uses simple geometry & basic colouring.
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.
Materia - Materia is a development environment to build advanced mobile and web applications.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
adapta-gtk-theme - An adaptive Gtk+ theme based on Material Design Guidelines - adapta-project/adapta-gtk-theme
Basecamp - A simple and elegant project management system.