nmap -O

Running (JUST GUESSING): Linux 2.6.X|2.4.X (90%), Microsoft Windows 2008|7|Vista (85%), MikroTik RouterOS 6.X (85%)
OS CPE: cpe:/o:linux:linux_kernel:2.6 cpe:/o:linux:linux_kernel:2.4.20 cpe:/o:microsoft:windows_server_2008:r2:sp1 cpe:/o:microsoft:windows_7::sp1 cpe:/o:mikrotik:routeros:6.15 cpe:/o:microsoft:windows_vista::- cpe:/o:microsoft:windows_vista::sp1

Aggressive OS guesses: Linux 2.6.18 - 2.6.22 (90%), Tomato 1.27 - 1.28 (Linux 2.4.20) (86%), Microsoft Windows Server 2008 R2 SP1 (85%), Microsoft Windows Server 2008 (85%), Microsoft Windows 7 SP1 (85%), MikroTik RouterOS 6.15 (Linux 3.3.5) (85%), Microsoft Windows Server 2008 or 2008 Beta 3 (85%), Microsoft Windows Server 2008 R2 (85%), Windows Server 2008 R2 (85%), Microsoft Windows 7 (85%)

No exact OS matches for host (test conditions non-ideal).
Network Distance: 2 hops
Service Info: OS: Windows; CPE: cpe:/o:microsoft:windows