Luminar Flex is another photo editing offering from Skylum (formally Macphun). One of the major criticisms of the direction of Luminar was that it was trying to replace Adobe Lightroom when in many cases users wanted the photo editing features of Luminar without the Digital Asset Management (DAM) capabilities.
In view of this, Luminar has listened to its users and is now offering two pathways for photo editing. The first pathway is to use Luminar 3 which incorporates the Luminar photo editor with DAM. This approach would be good for those users who don't have lightroom or a photo management tool and want to go down that path.
The second approach, which is that of Luminar Flex is to provide a plugin or standalone photo editing tool without a DAM (but only as an extension, so you still need an external photo editor). This means that those with Lightroom or Photoshop (and possibly even affinity photo) can use the photo editor functionality without the need for the integrated DAM. In brief tests following me contacting Skylum, I was able to obtain the photoshop plugin file and get this working with Affinity Photo (although it has not been designed for this function and performance is not guaranteed).
I personally think the dual approach is the right way to go, many people (myself included) have a workflow that is already fairly established so don't want to change their workflow because we are tired into using a specific photo editing package, having the ability to use Luminar as a plugin through Luminar Flex gives us the ability to take advantage of the fantastic AI photo editing capabilities without being bloated with (at least for me) an unneeded DAM.
Luminar Flex is available for free to all existing Luminar 2018 and Luminar 3 users or can be purchased separately for new users. Plugins will be removed from Luminar with Libraries in the next major release and will only be available in Luminar Flex.