Project Astoria (for converting apps from Android) is supposed to launch sometime during the summer, but no word on its official launch date (at least not publicly or that I can find by searching) yet.
Tools such as Project Astoria (for porting Android applications to Windows 10 Mobile), Project Islandwood (for compiling Objective C for Windows 10), and Project Centennial (for packaging native Windows desktop apps for the Windows Store), are not yet release-ready and no shipping dates have been announced.
http://www.theregister.co.uk/2015/06/29/visual_studio_2015_release_date/
The article does mention Visual Studio 2015 being made available on July 20th, though, so probably the earliest we can expect iOS and Android apps to pass through the Gates (or over the bridge, to use Microsoft's imagery

) to the other side is after that date. I'm not a developer, though, so I really don't know how long it will actually take for a flood of apps to show up... or if a lot of developers will start publishing Windows apps now.
Islandwood and/or Astoria are already in the hands of some developers.
Candy Crush Saga was a port using one of the new tools.