Z80SoC is a custom computer implemented in a FPGA. It is based on the Zilog Z80 processor, which is also implemented using a softcore - the widely used T80, available on opencores.org by Daniel Wellner.
This is not a finished project, as it needs a lot of development and basic resources such as SD/MMC card access and a fat filesystem. However, in terms of hardware it is far functional with inputs and outputs such as leds, keys, buttons, vga and keyboard.
The ROM can be developed in assembly Z80 or C. SDCC is a good development tool to use with Z80SoC.