Wrapper.java

public class Wrapper {
  public static String wrap(String s, int col) {
    return new Wrapper(col).wrap(s);
  }

  private int col;

  private Wrapper(int col) {
    this.col = col;
  }

  private String wrap(String s) {
    if (s.length() <= col)
      return s;
    int space = (s.substring(0, col).lastIndexOf(' '));
    if (space != -1)
      return breakLine(s, space, 1);
    else if (s.charAt(col) == ' ')
      return breakLine(s, col, 1);
    else
      return breakLine(s, col, 0);
  }

  private String breakLine(String s, int pos, int gap) {
    return s.substring(0, pos) + "\n" + wrap(s.substring(pos + gap), col);
  }
}

I find confusing the 3-arguments function breakLine. Furthermore, the gap argument looks like a flag for me and, as you pointed out in Clean Code, we must avoid flag arguments.

Would you do this kata differently nowadays?

I've cloned this gist and changed some things:
git://gist.github.com/1274003.git

This is a more efficient last-index computation for line 15:

int space = s.lastIndexOf(' ', col);