OStress is a Microsoft tool comes with RML utilities package and it uses to stress SQL Server. This is especially useful when you want to troubleshoot SQL Server while SQL Server is under heavy load.
It is a free tool for SQL Server developers and DBAs. It is designed to assist with performance stress testing of T-SQL queries and routines. The tool automatically collects metrics to help you determine whether your queries will perform under load, and what kind of resource strain they put on a server. In short, it also allows putting a serious load on your database.
OStress isn’t the easiest thing in the world to set up, but it works well.