WCH CH32V003 is a new ultra-cheap RISC-V microcontroller (MCU) clocked at 48 MHz with 2KB SRAM, 16KB flash, and a bunch of interfaces that sells for under 10 cents in quantities.
The MCU offers up to eighteen GPIOs, UART, SPI, I2C, an 8-channel 10-bit ADC, and several timers in TSSOP20, QFN20, SOP16, or SOP8 packages, and a small development board is also available.