Customize rectangle corners separately
You can currently round corners of squares by clicking and dragging to your desired radius. I wish I could:
1. only round certain corners (ie, only 2 not all 4)
2. enter the exact radius I want (used to be able to do that easily in the right panel, but that option has disappeared)- would be beneficial for handing off files to developers
Om Ashish commented
Hold alt key on windows or option key on mac and select drag the particular corner of the rectangle or square you want to make rounded.
Nomi: if you hold down Alt when dragging, it'll only affect that one corner.
nomi sum commented
One Enhancement would be:
Depending on the selection on the right (all corners vs. individiual corners) you should also be able to adjust individual corners by click-dragging.
Currently with clicking and dragging its ALWAYS *all* corners.
the latest release of XD (0.5.2.29 beta) actually does both of those things! Select a rectangle and check out the appearance panel on the right :)