Hybrid Child

Well, someone has to recomend this sooner or later anyways. First of all, both of them are Yaoi(Boys Love). They are from the same studio which also the reason their artwork is so (and even too) much similar. Specially main characters of both series (Ritsu and Kotarou) are *the same*. Both have cute romance in it, story is different thought. Anyways if you liked any of them, give the other a try. 

Very similar feeling and mood overall. About "robots" or non-humans that show emotion. Both are about tragic romances and use their emotional music very effectively. Both have a subtle, elegant slice of life feeling to them. 

similar art, but the story line and the characters are different also HC is more sentimental, so it hasn't a similar feeling about it 

Plastic Memories and Hybrid Child both have human-like 'dolls'. While Hybrid Child dolls 'reflect' the owner, Plastic Memories 'Giftias' have artificial souls with a limited lifespan of 9 years before they are retrieved. Plastic Memories is not a shounen ai, but both animes have bittersweet moments surrounded by the concept of 'love'. While Hybrid Child focuses on the doll growing from love, Plastic Memories deals with the memories of love when time is limited. 

Both are emotional, tear-jerking anime that drag you in and keep you captivated until the very last moment. Beautiful art, characters and soundtrack can be found in both. 

Both are short bittersweet stories that are executed in beautiful ways with unique characters and awesome music.  

Chobits is similar on the aspect of both being in a time where there are robots (for Chobits, Dolls/Robots for Hybrid Child) that can feel emotion and are loved dearly by their master's.