Avast now works without any issues in Windows 8.1. If Avast 8 has not worked for you in Windows 8.1 Preview, don’t worry! it works now without any issues or incompatibility warnings as Avast’s latest program update 8.0.1497 makes the free AV fully compatible with Windows 8 and Windows 8.1.
This release also fixes issues in virtualization module, script shield, and issued related to Outlook plugin. So if you’ve installed Windows 8.1 Preview, make sure you’re using Avast 8.0.1497 for it to work.
Read: Avast 2014 Beta review
Here are direct download links for Avast Free AV , of course these are for the latest version.
Source: Avast forum.