Acer have released their Aspire XC-115 desktop with FreeDos recently.  Although the price is fantastic, FreeDos will mean for most people having to install the Operating System like Windows for themselves.
If you install Windows 7 you will be missing some drivers as Windows cannot install them automatically.  Your front USB 3.0 ports won’t work and the resolution will be off.  Missing drivers include your Ethernet, PCI Encryption/Decryption Controller, SM Bus Controller and the Display adaptor will be set as Standard so that will need updating.
For your Ethernet driver you go to the Realtek website here and select one of the download links under the Windows 7 section.

Your USB 3.0 ports at the front are probably still not working at this stage.  To find these you download the Windows 8.1 Chipset driver from the Acer website here.  Select your make and model XC-115.  You’re looking for the category Chipset and the driver we know that works is version 13.352.1006.  Other versions may also work.
You also need the AMD R2 Display adapter.  Again on the Acer website download the VGA driver version 13.352.1006.0.
PCI Encryption/Decryption Controller you can download from Drivermax and even if you don’t pay for the full version you can still download one or two free drivers per day so make the most of it.  In Drivermax you want to install the AMD PSP 1.0 Device.  Also install the AMD SM Bus driver and this will install the SM Bus Controller driver.

You now have a fully operational Windows 7 Acer Aspire XC-115.