Good leather softeners include Leather Honey, Fiebing's, Kiwi Suede Protector, Lexol and Leather Nova. Different brands are best suited for finished, unfinished or suede leather.
Leather Honey is the best product for softening finished leather, according to The Leather Cleaner. Leather Honey brand has existed for decades and uses a nontoxic formula suitable for furniture and car interiors. Fiebing's Golden Mink Oil Leather Conditioner is a good product for unfinished leather products such as belts, and for suede or nubuck, Kiwi Suede Protector works well. Lexol Leather Conditioner and Leather Nova are effective conditioners which can be used on any leather except suede, says Best Leather Conditioner.