ITOT or iShares Core S&P Total US Stock Market ETF is an ETF issued by iShares. ITOT seeks to track high-performance stocks in the US S&P 500 market index.
ITOT: IShares Core S&P Total US Stock Market ETF
VTI: Vanguard Total Stock Market ETF
Vanguard is the largest portfolio manager in the US, and their securities tend to do quite well in the market. One of their most successful creations is VTI.