Recently Blackmagic introcuded the ATEM mini, a surprisingly powerful hardware switcher for around $300. While it's not going to replace man of the advanced features in OBS it has quite a bit of utility as a companion device. The Blackmagic site has a number of examples of how to use the ATEM in a traditional video production workflow, https://www.blackmagicdesign.com/products/atemmini/workflow. Since they've done such a good job we'll go over some flows that are more tailored to working with OBS
Streaming a show
The simplest workflow is to simply produce the show on the ATEM mini and use the video capture device in OBS to stream from there. The ATEM mini has a USB C port that when hooked up to a computer registers as a webcam in the OS. This is perfect for producing a show on the ATEM mini and using OBS to stream your production to various streaming services like Twitch or Youtube
Sub camera switching
The ATM mini can be used as a camera switcher while doing the rest of the show in OBS. This complements OBS well since sub switching is a feature that is often requested. The gist is that you hook up the cameras for your show to the ATEM mini, and embed the webcam output of the ATEM mini into an OBS scene. Then you can switch between different cameras but within the same scene in OBS.
Keyed browser overlays
In this example we'll be using OBS as a graphics generator to send keyed graphics from the browser to the ATEM mini. This requires not only the ATEM mini but also a Blackmagic decklink card, and most likely sdi -> hdmi converters. First of all load up a browser source with transparency, for this example I'm using the Muxy cheer bar.

Now configure your Blackmagic decklink card as an output with a keyer and click start to enable the decklink output

In the atem control software under upstream key set the Fill and Key source from the HDMI inputs on the ATEM mini that match the outputs on the decklink output. Then transition to camera 3.

You should now have a keyed browser output working in the ATEM Mini :)