The short answer is... not a lot of note. There are improvements to "Acrylic Material" (Micorosoft's new name for semi-transparency in the Windows UI), which make things slightly easier to live with, plus updates for Task Manager and Mixed Reality.
However, the biggest changes this week relate to Delivery Optimisation. Microsoft are really going to town on this feature (to recap, this is where your PC can download updates from other Windows PCs on your LAN, or on the 'net if you allow, and equally act as a streaming host to other PCs, a-la P2P networks) and in this build have added a whole skew of controlls allowing you to choose how much bandwith should be available to Delivery Optimisation; to view your download and upload statistics, plus many other tweaks and settings for these features.
There's also now a Windows Store item for installing Ubuntu on your Windows PC. I shit you not; MS are really into this Linux on Windows thing now, and reckon you should use their store *nix builds (other distributions are coming soon apparently) rather than trying to do the install yourself. It's actually quite a clever idea, as it keeps the uber-geeks happy that they can stare at a badly scaled text interface, while keeping the sysadmins happy that they're still supporting Windows as the underlying OS.
Full release notes are avaialable here: https://blogs.windows.com/windowsexperience/2017/07/13/announcing-windows-10-insider-preview-build-16241-pc-build-15230-mobile/#xMd5rXKSEdcpxrRq.97