The 40 mm square NEO from NanoPi manufactured by FriendlyARM has similar capabilities to the Raspberry Pi zero but powered by an Allwinner H3 32-bit Cortex A7 quad-core processor running up to 1.2 GHz with 256 or 512 MB RAM and a micro SD slot.

The NEO is the smallest board from the NanoPi series. Connectivity is taken care of with micro USB connector for power supply and OTG, USB 2.0 host type A and a 10/100 Ethernet port (100 Mbit/s). Additional I/Os include 24 GPIOs, serial UART, stereo line out audio and microphone input which are accessible via pin headers set on a standard 0.1 inch pitch. The processor includes a Mali400 MP2 GPU but the board lacks an HDMI output connector. The system runs u-boot and the Ubuntu Core OS.
 
With 256 MB the NEO retails at $8 and the version with larger memory is $11.