The best IDE alternative to Simulink is Ktechlab, which is both free and Open Source. If that doesn't work for you, our users have ranked more than 25 alternatives to Simulink, but unfortunately only one of them is a IDE.
Simulink alternatives are mainly Circuit Simulators, but if you're looking for
Electronic Design Automation Tools or IDEs you can filter on that. Other popular filters include
Free. You can also filter by region, for example
EU-based alternatives if you prefer software developed in the European Union. These are just examples - use the filter bar below to find more specific alternatives to Simulink.