ParagraphBuilder.cs

public class ParagraphBuilder
{
    public const int DefaultColumns = 86;

    private string _input;
    private int _columns;

    private int _remaining;
    private List<string> _output = new List<string>();
    private List<string> _line = new List<string>();
    private List<char> _word = new List<char>();

    public ParagraphBuilder(string input, int columns = DefaultColumns)
    {
        _input = input;
        _columns = columns;
        _remaining = columns;

        ParseInput();
    }

    private void ParseInput()
    {
        if (string.IsNullOrEmpty(_input)) return;

        foreach (var chr in _input.ToCharArray())
        {
            if (char.IsWhiteSpace(chr))
            {
                AddWordToLine();
            }
            else
            {
                _word.Add(chr);
            }
        }

        AddWordToLine();
        AddLineToOutput();
    }

    private void AddWordToLine()
    {
        if (_word.Count == 0) return;
        var word = string.Concat(_word);

        // Is there room on the line?
        if (_remaining >= _word.Count)
        {
            _line.Add(word);
            _remaining -= (_word.Count + 1);
        }
        // Is the word hyphenated and can the first part fit?
        else if (_word.Contains('-') && _remaining >= (_word.IndexOf('-') + 1))
        {
            var parts = word.Split("-", 2);
            _line.Add(parts[0]);
            AddLineToOutput();
            _line.Add(parts[1]);
            _remaining -= (parts[1].Length + 1);
        }
        else
        {
            AddLineToOutput();
            _line.Add(word);
        }

        _word.Clear();
    }

    private void AddLineToOutput()
    {
        if (_line.Count == 0) return;

        _output.Add(string.Join(" ", _line));
        _line.Clear();
        _remaining = _columns;
    }

    public override string ToString()
    {
        return string.Join(Environment.NewLine, _output);
    }
}

Converts a long string into a paragraph with breaks at the column width specified.
TODO:

• Break strings that are too long for the column width