https://play.google.com/store/apps/details?id=com.superiorin...

https://apps.apple.com/gb/app/repton-3-free/id895768027

It was one of my favourite games on our family's Acorn Archimedes in the early 1990s. I could play the first couple of screens on each of the ~40 themed level sets at age 7-8 or so, and sometimes the third screen, but then they became too difficult. I found it again at age 20 or so, and I could complete some of the level sets (8 screens in each), and I've gone back to it every 5 years or so, but there are still some puzzles I haven't solved.

Here's an early map (Finale screen B) from Repton 3 showing the complexity of the puzzles: https://www.reptonresourcepage.co.uk/GetMap.php?level=2&game... (via https://www.reptonresourcepage.co.uk/ )

A key difference with Boulderdash is in Repton, the diamonds don't fall if they're unsupported.