The number of devices you can run simultaneously will mostly depend on the product and plan you use.
Genymotion Desktop
There is no limit to the number of devices you run, but it is not recommended to run more than one device at the same time: Genymotion Desktop has not been designed to run devices in parallel - running more than one device at the same time will likely result in major performance loss, instability and memory leaks.
Genymotion SaaS (Cloud)
You can create as many recipes as you need, but the number of device you can run simultaneously will depend on your subscription plan.
You can only run 2 devices simultaneously with the default plan. If you need to run more, please contact sales@genymobile.com
Genymotion Device Image
You can create as many instances as you want, but there may be limits on the number of instances that can run simultaneously depending on your Cloud provider policy or restrictions.