This is the most powerful X68000 development tool in existence today. It is a fork of version 2.05 of PI's abandoned XM6 emulator. The changes are mostly user-interface related, and the focus is on development and debugging features rather than accuracy of emulation; however, it has enough general-interest improvements that I'm confident in recommending it over XM6 version 2.06 (the final official version).
Double-click the batch file named "Download XM6 Pro-68k" to retrieve and extract the necessary packages from XM6 Pro-68k site.