Well, it is not really retro/vintage since all the project is modern, but the Micromite Companion gives you all the feeling of a Retro computer.
“It’s a kit computer that is programmed in BASIC, capable of sprites, tiles, and SIDlike audio with 54K of programming space. The MMC also capable of communicating with serial, I2C, SPI, 1-wire, and other modern devices and sensors.”
Best of all, this board has a decidedly modern price — only $59 + reasonable shipping costs for the kit.
Source: Retrothing
Link: PropellerPowered