How to simultaneously execute scripts in bash

Question

I want to run a lot of scripts simultaneously in a bash script, with a for-loop. Example code:

#!/bin/bash
a=0
for a in (0..255)
do
  ./rleit.sh $a > res/$a.txt
done

I tried this with and without a . after the ./rleit.sh $a > res/$a.txt line. Also putting exec before that line does not run the scripts simultaneously.