The software can be downloaded from HERE.

What is Nvil:

Nvil is a polygon modeling application with rich tool sets. Its deep customization ability provides ways for user to create fast and comfortable workflow to suit individual needs.

Customizing UI can be a big tough task. It needs good modeling experience and knowledge of Nvil.
There are some user-created UI settings available in Nvil forum.

Features:

Pure Modeling:

Nvil is completely focused on modelling, which allows it to maintain a very clean UI and slimmed down tool-set, focused on just subdivision and polygon modelling. This not only allows Nvil to maintain a slimmed down tool-set, and UI but also allows for more development time to be spent on just the modelling tools and trying to make this the best 3d package available for that one use.

Extensive Customization:

Nvil allows for huge amounts of user customization, every tool and command can be rebound in the key editor, and the UI can be completely re-arranged. Nvil includes a powerful set of user customizable radial menus that are context sensitive and depended on the selection type. On top of all of this, even the way the user interacts with tools can be changed customized, with the help pf Nvils streamline tool editor.

AppLink:

Nvil has a built-in 3D-Coat app link.

Nvil also has clipboard copy/paste features which can be used to tranfer models between Nvil and other 3D applications if the corresponding application has the same clipboard features.

StreamLine Tools:

Streamline tools are unique to Nvil. They allow the user to create their own tools and change how they interact with existing ones, using existing commands and basic tools. These also allow for the tool-set to be slimmed down once again, since these are fully context sensitivity, so 1 tool can do a large variety of things depending on the circumstance. These also incorporate features like sticky keys, to make it extremely quick and easy to swap between tools.