I wanted to test my website if it can sustain strong DDoS's, but I don't know which tools could I use to simulate them in my website. What tools are used to simulate DDoS?
I found bonesi but it was last updated 2 years ago.
First you need to define what kind of attack you're trying to simulate.
Next pick (or write)tools that can be used to simulate that type of attack (HTTP Load Testing programs are often used, but there are dedicated tools out there as well. I'm not going to list them - you can Google as well as I can.)
Finally, run the attacks against your environment.
BIG IMPORTANT WARNING
You should schedule and announce your test window so users are aware of the possibility of an outage. Often simulations result in actual failures.
Under NO Circumstances should you run a DoS simulation/test attack against your environment without first notifying your hosting provider. This is especially true for external / full stack tests that will be going through your provider's network.
A 'strong' DDoS attack is highly relative to your environment, and would be near impossible to replicate by yourself if we're talking about a public website and not within a controlled environment. A DoS attack is one thing, in order to simulate a real Distributed denial of service attack you need a real test-bed of botnet(s) which I'm sure you don't own (<<). It's not difficult to find a free/fee-for-all botnets that you can use with certain 'off-hacker-sites' applications, but would/should you really trust these to not do more damage than you expect? The last thing you want is being in a hacker's radar, and/or associated with a vulnerable site.
IMHO, a good DDoS will always win... specially if you don't have the good disaster recovery/business continuation plan.
This is coming from someone who's lived through a DDoS (DNS amplification attack), it's no picnic and even though it's highly exciting, it's nothing you want happened to your network/website/host.
I don't have much experience with it, but take a look at LOIC (http://sourceforge.net/projects/loic/). You'll have to setup a number of clients, but you should be able to essentially DDoS yourself.