Jamul
I'm not gonna give much credit on gameplay here, since, well, it'd be hard to do a more exact clone of Lemmings! But it works well, it's well implemented. There's some really important stuff missing though, like countdowns, indications of how many to save, stuff like that. But it was still quite playable, and solvable and all. It died on me in the fourth? (where you had to dig down) level, I'm pretty sure because one of my sheeperings went off the right edge of the screen (left edge occurred safely in previous levels, however).
Sound would've added a lot, as would the typical lemmings particle deaths. Another nice thing would've been speed-up mode.