NetOcc

Open CASCADE Technology (OCCT) 8.0.1 for .NET: generated C# bindings with OCCT's names unchanged, one namespace per OCCT package (OCC.Core.gp, OCC.Core.BRepPrimAPI). One AnyCPU package for .NET Framework 3.5 and 4.5+, .NET 6, 8 and 10, with natives for win-x64, win-x86, linux-x64 and osx-arm64, and OCCT's documentation in IntelliSense.

dotnet add package NetOcc

// a 60 x 40 x 20 block with a hole through it
var block = new BRepPrimAPI_MakeBox(60, 40, 20).Shape();
var axis = new gp_Ax2(new gp_Pnt(30, 20, -1), new gp_Dir(0, 0, 1));
var hole = new BRepPrimAPI_MakeCylinder(axis, 8, 22).Shape();
var part = new BRepAlgoAPI_Cut(block, hole).Shape();

// round every edge by 1.5, each once
var edges = new TopTools_IndexedMapOfShape();
TopExp.MapShapes(part, TopAbs_ShapeEnum.TopAbs_EDGE, edges);
var fillet = new BRepFilletAPI_MakeFillet(part);
foreach (var edge in edges)
{
  fillet.Add(1.5, TopoDS.Edge(edge));
}

var rounded = fillet.Shape();

// its volume, then the part as STEP and, triangulated, as STL
var properties = new GProp_GProps();
BRepGProp.VolumeProperties(rounded, properties);
Console.WriteLine($"volume: {properties.Mass():F1} mm³");

var step = new STEPControl_Writer();
step.Transfer(rounded, STEPControl_StepModelType.STEPControl_AsIs);
step.Write("part.step");

new BRepMesh_IncrementalMesh(rounded, 0.1);
new StlAPI_Writer().Write(rounded, "part.stl");

Covered

All 362 packages of OCCT's FoundationClasses, ModelingData, ModelingAlgorithms, ApplicationFramework and DataExchange modules, and of Visualization's TKService, TKV3d, TKOpenGl (the driver) and TKMeshVS: geometry, topology, booleans, fillets, offsets, sweeps, shape healing, meshing, HLR, OCAF and XCAF documents, STEP, IGES, STL, glTF, OBJ, PLY and VRML, and 3D views.

Where to go

Start	Introduction: OCCT's layers and packages. Getting started: install, a first part.
Guide	Geometry, Topology, Modeling, Analysis and repair, Meshing, Files, Assemblies, Documents, 3D views
Concepts	From C++ to C#, Object lifetimes, Errors, How NetOcc works
Reference	Class index: every type, linked to OCCT's reference manual. Platforms, Building from source, Troubleshooting
Development	Design decisions, Pitfalls, Licensing, Skipped members

Every example on this site is compiled against the package on each change and run, except the on-screen 3D views, which need a window and a GPU.