Unity3D is an awesome game engine, and it's available for free for indie developers.
it also has a huge asset store where you can find almost everything, most of the plugins are paid, but some of them are available for free.
and bellow is a list of some of the best free Unity3D plugins.
1 - Unity-chan! model
This anime style model is good for prototyping a game, it includes ready to use 74 animations, poses and emotions!
This model is subject to a licence, please read it before use.
Need an inventory for your game character ? you can't find an easier way to implement it as the one proposed by "Inventory System".
Select your Character game object, click on "Setup" and voilà !
the plugin is easy to setup and configure, fully customizable and the source code is available and well commented.
Download Inventory SystemDownload Inventory System