There are various kits available to allow you to assemble a computer that’s compatible with various systems from the 80’s. Here are a few that I have found.
Getting a bit more up-to-date, the Harlequin is a clone of the ZX Spectrum. This is based on Chris Smith’s work on reverse-engineering the ULA, which he has released as a book. The bare PCB is available from various places such as ebay, and a full kit including components is available to buy from Byte Delight.
As always, let me know if you find any others in the comments.
Image Credits: fdecomite