This release doesn't hold a ton of new engine features, although the CrashReporter helps and there are some usability tweaks like graphic options and home/end for changing the view distance, along with the usual slew of bug fixes.
New modules include TerraTech & Machines by @Josharias, Rails by @small-jeeper, Breathing was extracted from core/engine by @Josephtsessions, and Signalling was put back in after finally getting fixed up for NUI
More details in the forum at http://forum.movingblocks.net/threads/stable-build-38-out-moar-modules.1063/