Just in time for holiday giving, Old Saybrook-based audio book publisher Tantor Audio is offering its entire catalog at 50 percent off. Merchandise includes bestsellers and award-winners in CD, MP3-CD and digital download formats. The sale also features more than a thousand titles priced at $6.99. Spend $25, and you’ll get free shipping. Order by Dec. 16 to get delivery by Christmas. Sale ends Dec. 31. Information: Tantor Audio.