First I noticed were leveraged exchanges like bitmex and bybit which offer up to 100x leverage.

I've seen there are margin options up to 4x on binance too (so you can lend 4x more than your balance and releverage from there).

Bitmex and binance both offer btcup and btcdown contracts which apparently releverage as they go so they don't liquidate (I'm not entirely sure how they work so you might want to take a look at them yourself).

Beyond that there are standard exchanges in the forex and stocks realm offering more traditional versions for btc too...