Gearset will work for any cloud that builds on core Salesforce.com platform, previously known as Force.com, using the Salesforce metadata format. This includes:
Sales Cloud (the core CRM of Salesforce)
Service Cloud
Salesforce CPQ (formally Revenue Cloud)
The Salesforce Platform
Commerce Cloud (the B2B managed package, formerly known as CloudCraze)
Revenue Cloud Advanced
Data Cloud
Salesforce Industries
Government Cloud
Health Cloud
Education Cloud
Energy and Utilities Cloud
Manufacturing Cloud
Consumer Goods Cloud
Financial Services Cloud
Media Cloud
Nonprofit Cloud
Marketing Cloud Engagement
We're talking about Marketing Cloud Engagement, the product formerly known as Exact Target. This isn't Marketing Cloud Account Engagement (Pardot) or Marketing Cloud Growth.
Note: Gearset's support also includes deployments happening between the above mentioned Salesforce clouds.
There are several Salesforce clouds that are actually entirely separate products, built on different underlying infrastructure - predominantly due to not using the Salesforce Metadata API.
Gearset does not currently work with these clouds:
Marketing Cloud Growth
Marketing Cloud Account Engagement (Pardot)
IoT Cloud
Commerce Cloud (the B2C Cloud which is a separate architectural stack)