Many centuries into the future, humans live as part of the Fractale system, a computer program that moderates their activity to ensure a free and peaceful existence. But while life is indeed comfortable, the cost of growing up in virtual reality communities filled with holographic people called 'doppels' means that it can also get lonely. For Clain living estranged from his parents, adventure finally knocks when he rescues a mysterious girl called Phryne, who appears to be on the run. She spends only a short time with him before hurriedly moving on but leaves behind an unexpected gift: the curious and frustratingly whimsical doppel called Nessa! As Clain learns to adjust to his new friend and survive the scrapes she gets him into, he discovers that she and Phryne are at the heart of a great conspiracy. If he is ever to gain a sense of purpose, Clain will have to leave his comfortable existence and challenge the only thing he has ever known, the Fractale system itself.
Koi Sento and Fractale are light (adventure?) sci-fi shows that are more concerned with cute/quirky characters and romantic comedy than fleshing out their stories (Koi Sento's flaws are more easily overlooked)
Ponyo is a goldfish who lives in the sea, and has an over-protective magician for a father. Soon Ponyo runs away from home and is rescued by a five-year-old boy named Sosuke. As she wants nothing more than to understand what it's like to be a human being, Ponyo uses magic to transform into a human girl, and the two begin to form a special bond. However, this magic results in drastic consequences, and one final test stands in Ponyo's way before she can truly be human. Can Ponyo fulfill her dream, or is she destined to return to the sea?
Ponyo and Fractale seem very similar to me. Maybe it is the overwhelming joyfulness of Nessa and Ponyo or the similarity in the themes, but I am confident that if you enjoyed one of these you will like the other.
Kanata Sorami, a young Private in the army, arrives in Seize to serve in the Clocktower Fortress and learn the trumpet under the tutelage of Master Sergeant Rio Kazumiya. Though peace hangs uneasily over the world, Kanata finds a relaxing routine of laundry, shopping, and trumpet practice greets her at her new post instead of brutal drilling and discipline. With help from the other members of the all-female 1121st Platoon, Kanata finds her place in the bustling city, bringing joy and humor to the war-weary residents while learning a great deal about the world.
I found the feel of these two series to be very similar. Both series feature a world that is at first glance idyllic and peaceful, but is over time revealed to be deeply scarred beneath the surface. Both Fractale and Sora no Woto also feature optimistic protagonists, similar art styles and unique European-style settings, as well a general lighthearted feel despite the dark themes also apparent in the show.
Kiba is a wolf, one of the last of his kind, and his dream is to find Paradise in a world torn asunder by war. Cheza, the legendary Flower Girl, can lead him to Paradise, but there are others who desire her, and help from other wolves at his side may not be enough. Driven by his noble spirit, he will not forsake his quest.
Wolfs Rain and Fractale are very different stylistically aside from a post-futuristic setting.
Wolfs Rain has a very serious tone as well as a lot more and better action sequences. If you are wanting the same level of action or same male testosterone, Fractale is not the best recommendation.
However if you enjoy exploring new sci-fi dystopic worlds, there are many similarities. Both animes also involve the main male 'protecting' an enigmatic female character who is somehow the key to everything, and the adventure and understanding of the story revolves around the male character(s) searching for the female one. Both animes thus revolve around the challenging of the current world order (whether intentionally or collaterally).
This recommendation is more if you just want more sci-fi social exploration than the action of Wolfs Rain. Also note that because Fractale is much shorter, the exploration of the world is not as in-depth.