AVG AntiVirus Free Beta is AVG's first release since the company was acquired by AVAST.
The program aims to blend the best technologies from each company. For example, the engine is AVAST, but the "Software Analyzer" heuristics come from AVG, and you also get AVG's ZEN device manager.
As this is the free build, functionality is limited to basic anti-malware, email scanning and web protection.
The beta also has some serious problems. In particular, the main scan doesn't check your system drive, forcing you to use the quick scan instead. In addition, heuristics are disabled on XP and Vista.
What's available looks good and seems easy to use, but with functionality holes like these we wouldn't recommending using it for long.
The new AVAST/ AVG hybrid will be an interesting product, eventually, but it's too early and limited a version to give any verdicts just yet. Don't try it anywhere that isn't fully backed-up, and even then, don't use it for long.