MeshLab is an open source system for processing and editing 3D triangular meshes. It provides a set of tools for editing, cleaning, healing, inspecting, rendering, texturing and converting meshes. It offers features for processing raw data produced by 3D digitization tools/devices and for preparing models for 3D printing.
As of MeshLab 2016.12, you can upload a mesh in PLY format directly to Sketchfab.
Open Meshlab's Global Parameters Window, find the Variable Name "MeshLab::Plugins::sketchFabKeyCode" and replace the Variable Value "0000000" with your API Token.
When your mesh is ready to upload, go to Filters → Quality Measure and Computations → Upload to Sketchfab. Enter a title, description, tags and mark it as Private and Published if necessary. In most cases, you should leave Auto Rotate enabled. Then, click Apply and your model will be uploaded to your account.