Atari 8-bit motherboard to fit the Atari 800XL case, it includes the main ideas of the cancelled 1450XL - designed to include a speech synthesis chip, PBI interface, and because it is a modern recreation it has optional space on the motherboard for installing modules for MIDI, UGV-II video, Sophia 2 mini-ldmi.

I'm sure you know about it from the AtariAge thread or bits of the past website.

Here is the Description

After completing the 1450XL Replica and 1250XL Remix boards I realized why stop there, why not go ahead and try to fit the most important features into a 800XL case. I was able to do that with just a little bit to spare. I was able to keep the additional feature set such as a Midi player and hooks for the addin boards PokeyMax 2B/4, UGV II and Sophia.

The 850XL will fit a normal 800XL case with almost no need to make any case mods. The 850XL retains all the features of the 1450XL except for the builtin modem, PBI parallel drive connector and RF Modulator. The 850XL has builtin hookups for the following addin boards, PokeyMax 2B/4, U178 Midi Player, Sophia and UGV II. The 850XL has the ability for PAL using the PALBurst board from @mytek, PAL OSC and PAL version ANTIC and GTIA chips. No additional soldering needed.