MCprep comes bundled with 25 fully rigged Minecraft models, but it will also let you add you own (non-Minecraft) assets.
The open-source MCprep addon makes creating Minecraft animations and sets near trivial and enjoyable. Even for non-Minecraft projects, the recent multi-character management tools are wonderful for asset management, often only found in paid-for addons.
The new features allow a user to simply point a path to a folder of different blend files containing character rigs. The addon creates a button for each character so you can one-click add a character to your scene, providing options like choosing to library link or append and clearing preset animation and poses. If you ever needed 20 instances of the same rig, this addon makes it easy to accomplish in less than 20 seconds!
For Minecraft animators specifically, the functionality is tenfold greater. The addon comes pre-packaged with over 25 fully rigged and animatable mobs from the game itself, created by many of the community's best known and respect Minecraft riggers. In addition to “mob spawning”, the addon has always provided sophisticated tools for making boring 3D Minecraft world imports into impressive, intricately modeled and properly materiale'd sets. I need not say more, simply watch the demo video to see what an asset this addon is!
The addon is actively being developed and has had releases at least every other week, and continues to be an addon created for and feature-driven by the community.