That must have been Nesticle in the early 2000's. That was the first time I realised how many crap games there were on the NES, long before the Angry Video Game Nerd began talking about that. However, Nesticle started my interest for Mega Man, so I bought the NES games later on, some as cartridges and the rest with the classic Mega Man collection for the PS2.
I was fascinated how good Nesticle ran on my old Pentium I computer. I was not fascinated by how some games like Castlevania III were unplayable due to graphics glitching.
Today, I use emulators mainly along with original cartridges plugged into the Retrode, as well as for some PCE CD games, until my Duo gets fixed again.