This is probably the best of the Fidelity Zero Fee funds. People flock to this fund because it covers the total stock market index.
FNILX: Fidelity ZERO Large Cap Index Fund
FZROX: The Fidelity ZERO Total Market Index Fund
This is probably the biggest and most popular of the Fidelity Zero Fee funds. It has one thing that everyone wants, the S&P 500.
This fund is the small-caps fund to pair with the large caps fund. At this point, you could combine FNILX and FZIPX and create the fund FZROX. Those two funds would be equal to 2500 companies.