Task: Forest fire
Java: import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

public class Fire {
	private static final char BURNING = 'w'; 
	private static final char TREE = 'T';
	private static final char EMPTY = '.';
	private static final double F = 0.2;
	private static final double P = 0.4;
	private static final double TREE_PROB = 0.5;
	
	private static List<String> process(List<String> land){
		List<String> newLand = new LinkedList<String>();
		for(int i = 0; i < land.size(); i++){
			String rowAbove, thisRow = land.get(i), rowBelow;
			if(i == 0){
				rowAbove = null;
				rowBelow = land.get(i + 1);
			}else if(i == land.size() - 1){
				rowBelow = null;
				rowAbove = land.get(i - 1);
			}else{
				rowBelow = land.get(i + 1);
				rowAbove = land.get(i - 1);
			}
			newLand.add(processRows(rowAbove, thisRow, rowBelow));
		}
		return newLand;
	}

	private static String processRows(String rowAbove, String thisRow,
			String rowBelow){
		String newRow = "";
		for(int i = 0; i < thisRow.length();i++){
			switch(thisRow.charAt(i)){
			case BURNING:
				newRow+= EMPTY;
				break;
			case EMPTY:
				newRow+= Math.random() < P ? TREE : EMPTY;
				break;
			case TREE:
				String neighbors = "";
				if(i == 0){
					neighbors+= rowAbove == null ? "" : rowAbove.substring(i, i + 2);
					neighbors+= thisRow.charAt(i + 1);
					neighbors+= rowBelow == null ? "" : rowBelow.substring(i, i + 2);
					if(neighbors.contains(Character.toString(BURNING))){
						newRow+= BURNING;
						break;
					}
				}else if(i == thisRow.length() - 1){
					neighbors+= rowAbove == null ? "" : rowAbove.substring(i - 1, i + 1);
					neighbors+= thisRow.charAt(i - 1);
					neighbors+= rowBelow == null ? "" : rowBelow.substring(i - 1, i + 1);
					if(neighbors.contains(Character.toString(BURNING))){
						newRow+= BURNING;
						break;
					}
				}else{
					neighbors+= rowAbove == null ? "" : rowAbove.substring(i - 1, i + 2);
					neighbors+= thisRow.charAt(i + 1);
					neighbors+= thisRow.charAt(i - 1);
					neighbors+= rowBelow == null ? "" : rowBelow.substring(i - 1, i + 2);
					if(neighbors.contains(Character.toString(BURNING))){
						newRow+= BURNING;
						break;
					}
				}
				newRow+= Math.random() < F ? BURNING : TREE;
			}
		}
		return newRow;
	}
	
	public static List<String> populate(int width, int height){
		List<String> land = new LinkedList<String>();
		for(;height > 0; height--){
			StringBuilder line = new StringBuilder(width);
			for(int i = width; i > 0; i--){
				line.append((Math.random() < TREE_PROB) ? TREE : EMPTY);
			}
			land.add(line.toString());
		}
		return land;
	}
	
	
	public static void processN(List<String> land, int n){
		for(int i = 0;i < n; i++){
			land = process(land);
		}
	}
	
	
	public static void processNPrint(List<String> land, int n){
		for(int i = 0;i < n; i++){
			land = process(land);
			print(land);
		}
	}
	
	
	public static void print(List<String> land){
		for(String row: land){
			System.out.println(row);
		}
		System.out.println();
	}
	
	public static void main(String[] args){
		List<String> land = Arrays.asList(".TTT.T.T.TTTT.T",
				"T.T.T.TT..T.T..",
				"TT.TTTT...T.TT.",
				"TTT..TTTTT.T..T",
				".T.TTT....TT.TT",
				"...T..TTT.TT.T.",
				".TT.TT...TT..TT",
				".TT.T.T..T.T.T.",
				"..TTT.TT.T..T..",
				".T....T.....TTT",
				"T..TTT..T..T...",
				"TTT....TTTTTT.T",
				"......TwTTT...T",
				"..T....TTTTTTTT",
				".T.T.T....TT...");
		print(land);
		processNPrint(land, 10);
		
		System.out.println("Random land test:");
		
		land = populate(10, 10);
		print(land);
		processNPrint(land, 10);
	}
}

VB: Public Class ForestFire
    Private _forest(,) As ForestState
    Private _isBuilding As Boolean
    Private _bm As Bitmap
    Private _gen As Integer
    Private _sw As Stopwatch

    Private Const _treeStart As Double = 0.5
    Private Const _f As Double = 0.00001
    Private Const _p As Double = 0.001

    Private Const _winWidth As Integer = 300
    Private Const _winHeight As Integer = 300

    Private Enum ForestState
        Empty
        Burning
        Tree
    End Enum

    Private Sub ForestFire_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.ClientSize = New Size(_winWidth, _winHeight)
        ReDim _forest(_winWidth, _winHeight)

        Dim rnd As New Random()
        For i As Integer = 0 To _winHeight - 1
            For j As Integer = 0 To _winWidth - 1
                _forest(j, i) = IIf(rnd.NextDouble <= _treeStart, ForestState.Tree, ForestState.Empty)
            Next
        Next

        _sw = New Stopwatch
        _sw.Start()
        DrawForest()
        Timer1.Start()
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        If _isBuilding Then Exit Sub

        _isBuilding = True
        GetNextGeneration()

        DrawForest()
        _isBuilding = False
    End Sub

    Private Sub GetNextGeneration()
        Dim forestCache(_winWidth, _winHeight) As ForestState
        Dim rnd As New Random()

        For i As Integer = 0 To _winHeight - 1
            For j As Integer = 0 To _winWidth - 1
                Select Case _forest(j, i)
                    Case ForestState.Tree
                        If forestCache(j, i) <> ForestState.Burning Then
                            forestCache(j, i) = IIf(rnd.NextDouble <= _f, ForestState.Burning, ForestState.Tree)
                        End If

                    Case ForestState.Burning
                        For i2 As Integer = i - 1 To i + 1
                            If i2 = -1 OrElse i2 >= _winHeight Then Continue For
                            For j2 As Integer = j - 1 To j + 1
                                If j2 = -1 OrElse i2 >= _winWidth Then Continue For
                                If _forest(j2, i2) = ForestState.Tree Then forestCache(j2, i2) = ForestState.Burning
                            Next
                        Next
                        forestCache(j, i) = ForestState.Empty

                    Case Else
                        forestCache(j, i) = IIf(rnd.NextDouble <= _p, ForestState.Tree, ForestState.Empty)
                End Select
            Next
        Next

        _forest = forestCache
        _gen += 1
    End Sub

    Private Sub DrawForest()
        Dim bmCache As New Bitmap(_winWidth, _winHeight)

        For i As Integer = 0 To _winHeight - 1
            For j As Integer = 0 To _winWidth - 1
                Select Case _forest(j, i)
                    Case ForestState.Tree
                        bmCache.SetPixel(j, i, Color.Green)

                    Case ForestState.Burning
                        bmCache.SetPixel(j, i, Color.Red)
                End Select
            Next
        Next

        _bm = bmCache
        Me.Refresh()
    End Sub

    Private Sub ForestFire_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        e.Graphics.DrawImage(_bm, 0, 0)

        Me.Text = "Gen " & _gen.ToString() & " @ " & (_gen / (_sw.ElapsedMilliseconds / 1000)).ToString("F02") & " FPS: Forest Fire"
    End Sub
End Class