A free program for Android, by Fast STL Viewer.

The Fast STL Viewer is an Android tool for viewing STL (Archive of Global Architecture and Building) files directly on your phone. The tool allows you to open your files from any of your devices (even from a USB drive). Once the model is opened, you can view its data as well as modify it.

In addition to viewing the data of your models, the app allows you to add new data to them and even to create new models from the same data. This way, you can easily archive and share your data with others.

Fast STL Viewer is a useful tool for those who need to view their models in 3D. It can be used for viewing purposes or for 3D printing. The app supports all the most common file formats.