ETFs are the best way to construct diversified portfolio. All different kind of asset classes.

Total Stock Market USA:
$VTI 
$ITOT

SP500:
$SPY
$VOO
$IVV

Nasdaq:
$QQQ

Total Stock Market International (ex-US):
$VEA
$IEFA

Total Stock Market Emerging Markets:
$VWO
$IEMG

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