The Unitree Aliengo is a medium-sized quadruped research robot weighing 21.5±1 kg without battery, measuring 0.65 by 0.31 by 0.6 m standing. It carries a 13 kg payload at over 1.5 m/s maximum walking speed, climbing slopes up to 25 degrees. Twelve high-performance servo motors with motor and output-end dual encoders per joint provide motion, with joint compound force control for full 3-axis attitude and position control across rugged gravel and grassland terrain. A 12,600 mAh battery provides 2.5 to 4.6 hours endurance. The developer version includes an onboard PC with open interfaces: 2 Ethernet, 2 USB 3.0, 1 USB 2.0, and 1 RS485 port, supporting user-mounted cameras, LiDAR, robotic arms, and GPS. Multi-view depth sensing uses 2 depth cameras with global shutter (minimum 0.11 m depth, 1,280 by 720 resolution) and 1 visual odometry camera with highly optimized V-SLAM (under 1 percent closed-loop offset, under 6 ms latency) and near-hemispherical 163-degree field angle fisheye lens. Four foot-end sensors, built-in intelligent air-cooling, wireless emergency stop, and fall protection are standard. Software control supports C/C++ and ROS with high-level and underlying interfaces allowing individual motor or leg control. Targets research applications.