First, it’s important to understand that smartthings is in the process of a huge transition: new hub, new app, new cloud platform. So the way in which integrations are currently done may be quite different from the way they will be done in the future.
To find out more about the new methods, it’s best to visit the new developer site:
To see examples of what’s being done now, there are a number which are quite popular.
1. The Dashboard Approach
There are two paid third-party dashboards, ActionTiles and SharpTools. Both are good, with a somewhat different set of features, and both have developers who are very active in these forums.
There are also a number of free dashboard offerings, basically code which people have developed for themselves and then shared with the community.
You can find discussion of all of these ( both paid and free) by going to the quick browse lists in the community – created wiki, looking down near the bottom of that page for the project report section, and then choosing the dashboard list.
2. The Workflow Approach
Separately, there have also been a couple of third-party offerings which include integration with smartthings. Stringify was probably the most popular free offering, but is no longer available. (It was bought by Xfinity to fold into their own interface.)
SmartRules was very popular through 2018, but the app has since been withdrawn because they were having troubles with the new platform.
Simple Control (formerly RoomieRemote) is a subscription-based service, somewhat expensive and mostly aimed at people with expensive home theater set ups, which has had their own smartthings integration for several years.
3. HomeKit Integration
And there are a couple of different iOS apps which are intended to combine HomeKit with SmartThings control. That includes switch and pushkit, but speaking just for myself, I don’t like the security framework for those so I haven’t really looked at them. (I’m not interested in opening up my HomeKit credentials to a third-party service.)