diff -r b9767cb5b06b -r d2bd73d28ff1 ui/cocoa/WindowManager.m
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ui/cocoa/WindowManager.m	Thu Dec 12 20:01:43 2024 +0100
@@ -0,0 +1,57 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2024 Olaf Wintermann. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#import "WindowManager.h"
+
+@implementation WindowManager
+
+static WindowManager *instance = nil;
+
++ (WindowManager*) sharedWindowManager {
+    if(instance == nil) {
+        instance = [[WindowManager alloc] init];
+    }
+    return instance;
+}
+
+- (WindowManager*)init {
+    _windows = [[NSMutableArray alloc] initWithCapacity:16];
+    return self;
+}
+
+- (void)addWindow:(NSWindow*)win {
+    [_windows addObject:win];
+    [win setDelegate:self];
+}
+
+- (void) windowWillClose:(NSNotification *) notification {
+    NSWindow *window = notification.object;
+    [_windows removeObject:window];
+}
+
+@end