What are some weight gain powders?

Thank you for the suggestions.but can anyone suggest me some additional protiens or carbohydrates powder,which I can take for gaining weight.as in powders which are available in the medical shops.eg.weight gain powders

I, personally, can't. These substances are not recommended - and I can't tell you *take this, this and this* because I can't gurantee you their effects (they might even be dangerous for your health). All I can tell you, from personal experience, that the safest way to gain weight is to slow down your metabolism little by little.
Also, you should go to a doctor (endocrinologist most probably) because you may have a health issue preventing you from gaining weight. By the way, have you always been so skinny? Have you suffered an eating disorder? How many calories / day do you eat? If you can give me more details, I could give you more infos too.
Anyway, if you're only skinny, but completely healthy, slowing down your metabolism will help you - all it's required is a bit of discipline.