Index: src/main/java/org/apache/jackrabbit/oak/explorer/Explorer.java
===================================================================
--- src/main/java/org/apache/jackrabbit/oak/explorer/Explorer.java	(revision 1645243)
+++ src/main/java/org/apache/jackrabbit/oak/explorer/Explorer.java	(working copy)
@@ -41,7 +41,10 @@
 import javax.swing.UIManager;
 import javax.swing.UIManager.LookAndFeelInfo;
 
-import org.apache.jackrabbit.oak.plugins.segment.file.FileStore;
+import org.apache.jackrabbit.oak.plugins.segment.file.FileStore.ReadOnlyStore;
+import org.apache.jackrabbit.oak.plugins.segment.file.JournalReader;
+
+import com.google.common.collect.Lists;
 
 /**
  * NodeStore explorer
@@ -64,7 +67,7 @@
         }
 
         final String path = args[0];
-        final FileStore store = new FileStore(new File(path), 256);
+        final ReadOnlyStore store = new ReadOnlyStore(new File(path));
         final boolean skipSizeCheck = args.length == 2
                 && skip.equalsIgnoreCase(args[1]);
 
@@ -90,8 +93,8 @@
         }
     }
 
-    private void createAndShowGUI(final String path, final FileStore store, boolean skipSizeCheck) {
-        final JFrame frame = new JFrame("Explore " + path);
+    private void createAndShowGUI(final String path, final ReadOnlyStore store, boolean skipSizeCheck) {
+        final JFrame frame = new JFrame("Explore " + path + " @head");
         frame.addWindowListener(new java.awt.event.WindowAdapter() {
             @Override
             public void windowClosing(java.awt.event.WindowEvent windowEvent) {
@@ -123,16 +126,46 @@
         JMenuBar menuBar = new JMenuBar();
         menuBar.setMargin(new Insets(2, 2, 2, 2));
 
-        JMenuItem menuCompaction = new JMenuItem("Tar Compaction");
-        menuCompaction.setMnemonic(KeyEvent.VK_C);
+        JMenuItem menuCompaction = new JMenuItem("Time Machine");
+        menuCompaction.setMnemonic(KeyEvent.VK_M);
         menuCompaction.addActionListener(new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent ev) {
-                int run = JOptionPane.showConfirmDialog(frame,
-                        "Run compaction on the tar files", "Tar Compaction",
-                        JOptionPane.WARNING_MESSAGE, JOptionPane.YES_NO_OPTION);
-                if (run == JOptionPane.YES_OPTION) {
-                    treePanel.compact();
+                List<String> revs = new ArrayList<String>();
+
+                File journal = new File(path, "journal.log");
+                if (!journal.exists()) {
+                    return;
+                }
+
+                JournalReader journalReader = null;
+                try {
+                    journalReader = new JournalReader(journal);
+                    try {
+                        revs = Lists.newArrayList(journalReader.iterator());
+                    } finally {
+                        journalReader.close();
+                    }
+                } catch (IOException e) {
+                    e.printStackTrace();
+                    return;
+                } finally {
+                    try {
+                        if (journalReader != null) {
+                            journalReader.close();
+                        }
+                    } catch (IOException e) {
+                    }
+                }
+
+                String s = (String) JOptionPane.showInputDialog(frame,
+                        "Revert to a specified revision", "Time Machine",
+                        JOptionPane.PLAIN_MESSAGE, null, revs.toArray(),
+                        revs.get(0));
+                if (s != null) {
+                    treePanel.revert(s);
+                    frame.setTitle("Explore " + path + " @" + s);
+                    return;
                 }
             }
         });
Index: src/main/java/org/apache/jackrabbit/oak/explorer/NodeStoreTree.java
===================================================================
--- src/main/java/org/apache/jackrabbit/oak/explorer/NodeStoreTree.java	(revision 1645243)
+++ src/main/java/org/apache/jackrabbit/oak/explorer/NodeStoreTree.java	(working copy)
@@ -62,12 +62,13 @@
 import org.apache.jackrabbit.oak.plugins.segment.SegmentNodeStateHelper;
 import org.apache.jackrabbit.oak.plugins.segment.SegmentPropertyState;
 import org.apache.jackrabbit.oak.plugins.segment.file.FileStore;
+import org.apache.jackrabbit.oak.plugins.segment.file.FileStore.ReadOnlyStore;
 import org.apache.jackrabbit.oak.spi.state.ChildNodeEntry;
 import org.apache.jackrabbit.oak.spi.state.NodeState;
 
 public class NodeStoreTree extends JPanel implements TreeSelectionListener {
 
-    private final FileStore store;
+    private final ReadOnlyStore store;
 
     private DefaultTreeModel treeModel;
     private final JTree tree;
@@ -79,7 +80,7 @@
     // TODO make this configurable
     private final boolean cacheNodeState = false;
 
-    public NodeStoreTree(FileStore store, JTextArea log, boolean skipSizeCheck) {
+    public NodeStoreTree(ReadOnlyStore store, JTextArea log, boolean skipSizeCheck) {
         super(new GridLayout(1, 0));
         this.store = store;
         this.log = log;
@@ -577,38 +578,8 @@
         log.setText(sb.toString());
     }
 
-    public void compact() {
-        sizeCache = new HashMap<RecordIdKey, Long[]>();
-        treeModel = null;
-
-        StringBuilder sb = new StringBuilder();
-
-        long s = System.currentTimeMillis();
-        store.compact();
-        try {
-            store.flush();
-        } catch (IOException e) {
-            sb.append("IOException " + e.getMessage());
-            e.printStackTrace();
-        }
-        s = System.currentTimeMillis() - s;
-
-        sb.append("Compacted tar segments in " + s + " ms.");
-        sb.append(newline);
-
-        sb.append("File Index");
-        sb.append(newline);
-
-        List<String> files = newArrayList(store.getTarReaderIndex().keySet());
-        Collections.sort(files);
-
-        for (String path : files) {
-            sb.append(path);
-            sb.append(newline);
-        }
-        sb.append("----------");
-        log.setText(sb.toString());
-
+    public void revert(String revision) {
+        store.setRevision(revision);
         refreshModel();
     }