An STL editor can
- repair STL files, e.g. fill holes, repair flipped triangles, bad edges, etc.
- Merge STL files
- Create STL files from other formats
- Do some simple constructions, e.g. subtractive geometry or adding simple parts.
STL files are used in 3D printing.
- STL specific
- Netfabb Studio (free) and Netfabb Pro (expensive). Netfabb was the first easy to use commercial product.
- Magics from Materialise
- Meshmixer. A free tool from Autodesk for meshmixing, sculpting and support generation. If your slicer cannot produce a good support structure, try this. Also useful to eliminate useless internal structures.
- All-in-one tools
- Other tools that could be useful