Works on all versions of Minecraft from 1.6.4 up to 1.10.2. Features a configurable xray mode and cave finder, fullbright, configurable coordinates display, survival fly and fly speed.
You can download it here. (No adfly, direct link)
The latest version of XRay is version 33. It was released on Oct 9, 2016
How do I install it?
The mod comes with an installer. Simply double click on the downloaded Jar, and select a profile to install it into.
Note: if you double click on the installer, make sure to Open with ~> Java(TM) Platform SE binary. If that option is not available you may need to install or reinstall Java.
How do I change what blocks are visible?
All configuration is done through the user interface. The default keybinding to open the user interface is J, which you can change in-game if needed.
It turns out that getting a complete list of all blocks in the game, especially when third party mods are involved, is a bit difficult. XRay will prepopulate the list with some blocks it can easily detect, however, some may still be missing. To address this problem, XRay will add the missing blocks to the list as it filters them when XRay is enabled.