Gatling is a widely used load testing tool that is maintained by Gatling Corp. By default, we use version 3.2.1 on our grids. However, we do also support 2.3.1 and can switch you over if you need that.
Gatling scripts are written in Scala. There are some modifications necessary to run Gatling on Flood depending on which version of Gatling you're using. Our getting started guide contains a sample script for Gatling 3.0.