I want to provide tooltips for the UI buttons, but obviously a "hoverable" tooltip will not display on a touch device. what is an alternative way to display the same information as a tooltip (in this case, a short description of the buttons "Select", "Move", "Resize" etc.)
Add a help icon, when you tap it show a help overlay.
Something like this, change to fit your needs obviously.
Unfortunately, the best usability for the users is to include text labels (even for non-mobile UIs as well). See http://www.nngroup.com/articles/icon-usability/. It doesn't look like you have a lot of space, so I imagine you would include labels if you could.
Given your current design, I would add a prominent label that describes the selected tool (i.e. "Currently using: Select Tool"). Hopefully your users would be familiar with this kind of editor UI and would be willing to select all the different available tools to see what the label said (and thus, what the icon meant).
Why not show the default tooltip on extended press? This is how Google Analytics (SE too) shows its tooltip. If you press the "Create segment" icon you will see the tooltip as below in Android.
Also users' "burden of learning new controls" is also waived. They will naturally try the default option first.
Moments for example.) Apple doesn't use tooltips as far as I know.
You could translate hover into mobile tap-and-hold: Pinterest mobile team has developed a tap-and-hold popup menu for iOS app that works like hover for mobile. http://www.cnet.com/news/pinterest-adds-animated-pinning-shortcut-to-ios-app/
