We have just posted a great new custom FireMonkey Windows 10 style that you can use to build Windows 10 apps with RAD Studio XE8 right now.
With the full release of Windows 10 being right around the corner, this is a great time to start building apps for Windows 10. You can apply the Windows 10 style to your existing FireMonkey apps and new FireMonkey Windows applications using the StyleBook component.
You can download the new FireMonkey Windows 10 XE8 style here.
For the VCL Windows 10 style...