Who/what is able to trade equities specifically (like SPY the ETF, or any of its underlying components like AAPL, META, etc.) pre-market and/or post-market?
Anyone that uses IBKR as their broker can trade what I mentioned above pre/post market (and some cases overnight). IBKR is a retail broker. I use them, for example. Most brokers in the US let you trade common stock before and after market hours, even ones like webull. That said, not every broker has the same pre/post market trading hours, but the better ones let you trade almost all day and night depending on the underlying equity.
Enough to dedicate an 60-90mins of my day to scalping one or two trades and then go about my day as usual. I have a consistent strategy I backtested and follow. I don't see a trade that meets my criteria, then I close my broker. Most people that day trade don't do that and that's why they lose money.
I've been trading for a while and don't suggest to others to trade futures[0]. It's essentially highly leveraged stock, but less risk than options.
Any investor can. If the option is not available to you, contact your brokerage to ask about it. Many (most?) brokerages require signing a waiver confirming that you understand the additional risk posed by trading in low-volume pre- and post-market yours.
https://www.interactivebrokers.com/en/?f=%2Fen%2Ftrading%2Ft...
https://ir.cboe.com/news-and-events/2021/06-15-2021/cboe-ext...
https://www.reddit.com/r/options/comments/xr3gqb/where_can_i...