Obaku Zen is a unique blend of Zen and Pure Land elements that originated in China and was brought to Japan in the 17th century by the Chinese monk, Ingen. This form of Zen is often referred to as the "third sect" of Zen, alongside Rinzai and Soto, and has distinct differences from other forms of Zen.

One of the key differences of Obaku Zen is its incorporation of Pure Land elements. Pure Land Buddhism is a separate branch of Buddhism that emphasizes the practice of devotion and recitation of the name of the Amitabha Buddha. In Obaku Zen, this element is integrated into the practice of zazen, or seated meditation, where practitioners recite the name of the Amitabha Buddha as a way to focus the mind and cultivate mindfulness.

Another distinguishing feature of Obaku Zen is its use of koans, or paradoxical riddles, in its practice. While other forms of Zen also use koans, Obaku Zen places a greater emphasis on them as a means of awakening to one's true nature. In fact, the founder of Obaku Zen, Ingen, was known for his mastery of koans and his ability to use them to guide his students towards enlightenment.

Obaku Zen also has a unique approach to meditation. While other forms of Zen prioritize sitting meditation, Obaku Zen emphasizes the importance of both seated and walking meditation. This is in line with the teachings of Pure Land Buddhism, which encourages the practice of mindfulness in all activities, not just during seated meditation.

One of the most notable differences between Obaku Zen and other forms of Zen is its organizational structure. Unlike Rinzai and Soto, which are monastic traditions, Obaku Zen is more lay-oriented and allows for the ordination of married priests. This has allowed for a wider accessibility to the practice of Zen, as it is not limited to those who are willing to renounce their worldly lives.

In terms of philosophy, Obaku Zen also differs from other forms of Zen. While all forms of Zen emphasize the concept of emptiness and the idea of non-duality, Obaku Zen places a greater emphasis on the Pure Land concept of "other-power," or the belief that one's enlightenment is not solely dependent on one's own efforts, but also on the grace and guidance of the Buddha.

In summary, Obaku Zen stands out from other forms of Zen due to its incorporation of Pure Land elements, emphasis on koans, unique approach to meditation, organizational structure, and philosophical beliefs. Its blend of Zen and Pure Land elements has attracted many practitioners over the years and continues to be a significant form of Buddhism in Japan and beyond.