I wrote server programs which each binds to the same endpoint.

    try (var executor = Executors.newVirtualThreadPerTaskExecutor();
         var server = new ServerSocket()) {
        {
            try {
                server.setOption(StandardSocketOptions.SO_REUSEADDR, Boolean.TRUE); // IOException
            } catch (final UnsupportedOperationException uoe) {
                log.error("failed to set {}", StandardSocketOptions.SO_REUSEADDR, uoe);
            }
            try {
                server.setOption(StandardSocketOptions.SO_REUSEPORT, Boolean.TRUE); // IOException
            } catch (final UnsupportedOperationException uoe) {
                log.error("failed to set {}", StandardSocketOptions.SO_REUSEPORT, uoe);
            }
            server.setReuseAddress(true); // SocketException
        }
        {
            assert !server.isBound();
            server.bind(_Constants.SERVER_ENDPOINT_TO_BIND); // IOException
            log.info("bound to {}", server.getLocalSocketAddress());
            assert server.isBound();
        }
        {
            __Utils.readQuitAndClose(true, server);
        }
        while (!server.isClosed()) {
            final var client = server.accept(); // IOException
            executor.submit(() -> {
                try {
                    log.debug("accepted from {}", client.getRemoteSocketAddress());
                    for (int r; (r = client.getInputStream().read()) != -1 && !server.isClosed(); ) { // IOException
                        log.debug("discarding {} received from {}", String.format("0x%1$02X", r),
                                  client.getRemoteSocketAddress());
                    }
                } finally {
                    client.close();
                }
                return null;
            });
        }
    }

On macOS multiple processes work. And Windows won't let it.

How can I make Windows allow multiple JVM processes bind on the same socket address?

Here comes what I get when I start a second process (on Windows).

21:36:02.588 [                main] ERROR - failed to set SO_REUSEPORT
java.lang.UnsupportedOperationException: 'SO_REUSEPORT' not supported
    at java.base/sun.nio.ch.ServerSocketChannelImpl.setOption(ServerSocketChannelImpl.java:219)
    at com.github.onacit.rfc863.Rfc863Tcp2Server.main(Rfc863Tcp2Server.java:25)
Exception in thread "main" java.BindException: Address already in use: bind
    at java.base/sun.nio.ch.Net.bind0(Native Method)
    at java.base/sun.nio.ch.Net.bind(Net.java:565)
    at java.base/sun.nio.ch.ServerSocketChannelImplBind(ServerSocketChannelImpl.java:344)
    at java.base/sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:301)
    at java.base/java.nio.channels.ServerSocketChannel.bind(ServerSocketChannel.java:224)
    at com.github.onacit.rfc863.Rfc863Tcp2Server.main(Rfc863Tcp2Server.java:33)

Process finished with exit code 1