NicoNico Solid is a sub website of NicoNico intended for posting 3D models and renders. You can upload a .zip file of a model, and it'll be displayed in a 3D view which can be zoomed in and out. You can also adjust the lighting, select a pose or motion, and set the model to be up for download along with specific terms for the model.
There are two categories, edited models and full scratch models. Edited models are for things like retextures, assembled models, etc. Full scratch is for models made 100% by the uploader. It is also possible to post 3D model renders as well. You can also put motions and poses for download too.