Orange Pi is a provider of a variety of Rockchip, Allwinner, and MediaTech processor based devices with different prices and capabilities along with the open source software to run on those devices. The three most common products listed by increasing price and capability are: Orange Pi Zero, Orange Pi 3B, Orange Pi 5, and Orange Pi 5 Plus.
A variety of Linux based operating systems are available with Android, Ubuntu, Debian, and Orange Pi OS being the most common. The WoR Project is working on supporting Windows for ARM for the Orange Pi 5 boards similar to what they did for the Raspberry Pi.
Orange Pi devices can be purchased from AliExpress and Amazon with various vendors offering bundles that include not only the board but power supply, case, heat sinks, etc. Some of the products have WiFi and Bluetooth built into the board and some require an additional WiFi/BT module. The boards have a microSD card drive and the larger, more expensive boards have a connector for EMMC flash. The more expensive boards also have a PCIe M.2 SATA connector allowing for an NVMe drive to be installed on the board.
The boards have an HDMI connector though with some such as the Orange Pi Zero the connector is mini HDMI. Larger boards also have a camera interface and an integrated RKNN NPU AI accelerator. Most boards have a 40 pin connector similar to the Raspberry Pi though the pin definitions are different.
As a support concern, the Orange Pi community is not as large as that for the Raspberry Pi so getting questions answered or assistance with problems can be difficult.