Every single bot that works; from your script kiddie's basic python script to professional bots you can buy.
It would be awesome to have exchanges work without showing buy and sell walls up to a single satoshi but the lack of transparency wouldn't worth it.
But still, coins with let's say a value of 5532 sats only showing on exchanges as 5k sats for buy and 6k sats for sell would render most bots useless.
I don't care for arbitrage bots, good for them for noticing the discrepancy but price manipulating bots are a serious cancer to cryptos.
It's impossible to tell what the real volume of these coins would be if it was left up to manual trading. ETH generates over 90% of it's volume from bots on Poloniex and same for many other coins but it doesn't reflect true interest.
