Is there a Wii homebrew that allow you to send .nds files to your DS using the Nintendo DS download and play?

Is there a Wii homebrew that allow you to send .nds files to your DS using the Nintendo DS download and play, like in the Nintendo Channel on the Wii?

No, and there never will be.
It does not work that way.

Can I have some explainetions about it, please? What do you mean when you say that "It does not work that way"?

Full .nds games run from a cartridge. Download Play titles run exclusively inside RAM.

While metroid_maniac is correct that there is not such an app, he is not (completely) correct that such an app is impossible. The original DS (the "Phat" with the very first firmware version, v1) can load homebrew apps sent to it via Download Play (via a tool called "Wireless MultiBoot" or WMB). Later versions of the firmware (found on newer Phats and all Lites) fixed the bug exploited for this, but they can have a custom firmware called "FlashMe" installed which would allow WMB to work again. However, installing this custom firmware risked bricking the device, so isn't really worth it now (it did have other advantages but they're now mostly redundant).

In theory, I'd guess that an app could be written to send apps via this WMB protocol to v1 firmware and FlashMe'd DS consoles, but there's not much point really. There are much simpler methods of loading homebrew (and better; with WMB you can't save data in homebrew e.g. game saves etc., but with other methods you can), and this will only work on a very slim subsection of DS consoles anyway.