VisualStl

Most CAD applications designed to handle 3D models can open and edit STL files, but a lightweight utility is more suitable when you only wish to analyze a particular model or perform some basic modifications.
VisualStl is a straightforward and fully portable application that allows you to view these models, as well as scale or rotate them. It offers multiple visualization modes, including a horizontal slicer, and it is very easy to use.

Handy STL viewer that includes a few basic editing tools

After importing a model, you can choose from one of the four available viewing modes available in the toolbar. These include a horizontal slicer, which can be used to cut the model into multiple parts and perform a more detailed analysis.
If you only wish to view the model without editing it in any way, you can zoom in our out with the help of the mouse wheel and rotate the object with simple mouse movements.
However, it is also possible to perform permanent modifications by rotating or scaling the model along any of the three axes.

Lightweight tool that can be used on the go

While VisualStl clearly does not offer an extensive array of features, it is a great choice for users who need a simple, no-frills utility that enables them to open and edit STL files.
The application does not need to be installed on your computer before use, which means the single executable file can be stored on a USB drive and deployed whenever it is required.
Moreover, no additional data is stored on your PC when running VisualStl, so no traces will be left behind when deleting the program.

Straightforward STL viewer and editor that features a minimalistic interface

When taking everything into consideration, VisualStl is a lightweight, no-nonsense application that does the job it was designed for without unnecessary complications. It enables you to view STL 3D binary files, as well as perform some small modifications, and it features a streamlined, intuitive UI.