This is a semi-cycle accurate 6502 CPU emulator. It implements all known opcodes only. Decimal mode arithmetics are also implemented. The C flag is valid in decimal mode while N, V, Z is not valid as per the original 6502 implementation.
This application also include a web-based debugger to inspect the internal state of the CPU and memory. It is a Flask web app.
Enter - Run Code Continuously
Space - Step one instruction
T - Skip N operations (without displaying it to the debugger. This makes it run at full speed)
R - Reset CPU (Does not reset memory)
S - Stop Continuous Run
One Lone Coder's excellent tutorial at OLC NES
Bruce Clark's decimal mode write up at 6502.org
Opcodes Reference at 6502.org
Instructions Reference at obelisk.me.uk