The Power of Now is about living in the present moment so you suffer less and have more inner peace. It's really about reconnecting to your physical senses rather than being lost in thinking. Eckhart Tolle says past and future are only mental simulations because your life always happens Now.
The Heart of the Buddha's Teaching introduces the most essential Buddhist ideas in a way even secular people can easily digest. These ideas include The Four Noble Truths and The Noble Eightfold Path. Thich Nhat Hanh explains how Buddhism is in its essence a pragmatic approach to ending personal suffering.