Build 10136 include improvements to Cortana and Photos and Camera, according to a June 16 blog post outlining the changes in the new build. There are also lots of "subtle" changes in the interface, including modifications designed to make Windows Phones with screen sizes of five inches or more easier to use with one hand. The new build also includes a number of bug fixes.
With this build, Microsoft has not added any new Windows Phones to the list of those the preview already supports.
Today's build is available only to select phones running Windows Phone 8.1 that have opted into the Fast Ring. That means those on the previous test build (10080) need to go back to Windows Phone 8.1 using the Windows Phone Recovery tool first. Those on Build 10080 who opt not to flash back to WP 8.1 won't get this build, but still will get whatever follows 10136. It's worth reading the blog post for more detailed instructions about installing today's new build.
Windows 10 Mobile won't be available in final form starting July 29 -- the beginning of the rollout of Windows 10 for PCs. It will "release broadly later this year," Microsoft officials continue to say.