Like Google and Apple, Kobo uses its own unique form of the Epub ebook file format. Google's file format has no known name, and of course Apple uses iBooks, but Kobo's take is called Kepub.
Since Kobo also support Epub, there's little reason to bother with Kepub (other than stripping the DRM from the ebooks you buy from Kobo). But if you want to convert your ebooks to Kepub you now have a new option.
Kepubify is a free app for Windows, Linux, and macOS that will take your DRM-free Epub file and turn it into a Kepub. Linux and macOS users will have to put a little work into setup, but Windows users will be able to simply download the EXE file and then drag an Epub file on top of it. The ebook will be converted automatically (this also works for a folder of Epub files).
I am not sure that I would want to bother, though; Epub works just fine on Kobo's devices, and there are only a few software features ( image zooming, footnote previews, and an estimated reading timer) that Kobo supports in Kepub but not Epub.
Kobo ereaders are also supposed to be faster at displaying a Kepub file, but I have not seen that.
You can download Kepubify from the link below.