The shareware version of Megaboulder is a straight to the point Boulderdash clone. It requires EGA and runs fine on 8086/8088 systems. Megaboulder comes with a built-in level editor, so you can create your own maps! In the shareware version you have just 'one screen' to play in (which is great, actually) whereas the full version scrolls along. I prefer the shareware way.
You can download the original shareware here: Megaboulder 2.0 shareware. A modified version can be found here: Megaboulder 1.1 shareware ('right click > save as' in case it doesn't work). Inside the ZIP-file you'll find 3 versions, mega 1 being easiest and mega 3 is the most difficult one. Notice that these are not the original levels made by Richard Schabath!
Screenshots (3 in-game, 1 editor):
Tip on playing this using DOSBox: configure the game to 'Sehr langsam' when playing in DOSBox with 3000 cycles.
In-game video of the original Megaboulder 2.0: