A Phoronix reader wrote in this week to share lowRISC, a hardware platform aiming to be open-source from its System-on-a-Chip (SoC) to the development boards. As implied by the name, lowRISC is based upon the 64-bit RISC-V instruction set.
While pricing or expected availability has yet to be shared, lowRISC is aiming to deliver a low-cost development board of the platform. LowRISC is operating as a not-for-profit organization aligned with the University of Cambridge, of whom many of the team members are staff members of the university. Several of the team members also have ties to the Raspberry Pi.
There isn't much to share yet but you can learn more at lowRISC.org.