I was a premium user of Tabs Outliner a few years back. I very much liked its hierarchical tree model and browser control. Particularly for that point in time it was a very nice piece of work.
Recently I've been developing a quite different tool but with a similar tree structured data model and ability to control the browser. I've been focusing on building not marketing but have generated some enthusiastic support from users even in advance of the 1.0 version. I had some TO users request imports into BrainTool, my extension, so I implemented an ability to do that.
From surveying the activity on the Google Group and userecho site it seems like the Tabs Outliner project is somewhat moribund, but with a number of active and often frustrated users. As you probably know Tabs Outliner will stop working at the end of the year. I think BrainTool is a good match for those peoples needs and having them as users might enable it to evolve faster than it would otherwise.
Are you interested in open sourcing or selling Tabs Outliner? I would like to offer a migration path to BrainTool and the potential for the TO source code to be ported to Manifest V3 such that it can continue to work in 2023.
Thanks for your consideration,
Customer support service by UserEcho