Seeking Free Opensource Shapefile Writer for .NET

I feel your pain. I went through the same sort of thing with NetTopologySuite (v1.13) and had some success looking at the unit tests.

First off, you might check out the DotSpatial library which was referenced in a similar question specific to DS shapefile operations

I am personally happy with the NTS library. Once you figure out the object model it's not too much fuss to put something together. Since this topic will likely be referenced more than once here is a quick code dump for writing shapefiles from NTS.

1) Download the NTS (1.13.0) Binaries

2) Reference the following assemblies:

-GeoAPI, NetTopologySuite, NetTopologySuite.IO, NetTopologySuite.IO.GeoTools (guess how long it took to figure out this last one was required)

3) Write some code (this is a 10 minute hack job)

add using statements for NetTopologySuite, NetTopologySuite.IO, NetTopologySuite.Features, GeoAPI, GeoAPI.Geometries (sorry I can't figure out how to get SO to format these)

        string path = @"C:\data\atreides";
        string firstNameAttribute = "firstname";
        string lastNameAttribute = "lastname";

        //create geometry factory
        IGeometryFactory geomFactory = NtsGeometryServices.Instance.CreateGeometryFactory();

        //create the default table with fields - alternately use DBaseField classes
        AttributesTable t1 = new AttributesTable();
        t1.AddAttribute(firstNameAttribute, "Paul");
        t1.AddAttribute(lastNameAttribute, "Atreides");

        AttributesTable t2 = new AttributesTable();
        t2.AddAttribute(firstNameAttribute, "Duncan");
        t2.AddAttribute(lastNameAttribute, "Idaho");

        //create geometries and features
        IGeometry g1 = geomFactory.CreatePoint(new Coordinate(300000, 5000000));
        IGeometry g2 = geomFactory.CreatePoint(new Coordinate(300200, 5000300));

        Feature feat1 = new Feature(g1, t1);
        Feature feat2 = new Feature(g2, t2);

        //create attribute list
        IList<Feature> features = new List<Feature>() { feat1, feat2 };
        ShapefileDataWriter writer = new ShapefileDataWriter(path) { Header = ShapefileDataWriter.GetHeader(features[0], features.Count) };

        System.Collections.IList featList = (System.Collections.IList)features;
        writer.Write(featList);

So, not well documented but it is fairly point & shoot once you get going.

I haven't used it myself but quickly looking at the documentation for DotSpatial, it looks like it should be able to do what you want.

It has individual assemblies up on NuGet if you know which ones you need (which I don't).

Here is a sample that at least demonstrates the possibility. It would be nice if there was a WKT reader/converter to make for a more readable sample, but that seems to be missing.

There is also shapelib: http://shapelib.maptools.org/

A .NET wrapper is listed on the webpage.