Thanks.

How does it differ from a typical outline editor?

I worked with Ecco Pro for about ten years, which was the best available outliner at that time; there were some others, e.g. the OmniOutliner on Mac, which were either on the wrong platform (for me) or not powerful enough. It’s a good question what a “typical outliner” means. As a common denominator it’s just a text editor with indented paragraphs which can be closed on demand and have some formatting features. Ecco Pro - and also CrossLine - are integrated with a (hierarchical) database so whatever you type is automatically saved. CrossLine exceeds the capabilities of Ecco Pro in different ways; it’s based on Qt (now LeanQt) and thus cross-platform (Ecco was windows only and Omni Outliner Mac only); it can have as many outlines as required, and the outlines can be docked and kept visible like in a tiled window manager (most other products just support one big outline per file); it also supports cross-links within the same CrossLine repository, or over different CrossLine repositories; the former can be “transclusive”, i.e. they represent a live view of the referenced item, but integrated in the text flow of the item containing the reference (thus the term “transclusion”, see also https://en.wikipedia.org/wiki/Transclusion). There are some more important features, but the ones mentioned allowed me to use CrossLine for all of my projects (among them some big government defence procurement projects) as a notebook for facts, minutes, results, action items and whatever unstructured information drops in during a project or daily life, but also for requirements management and specification development. CrossLine can cope with large outlines and databases, which becomes very slow with many other outliners I tried.

CrossLine is a true intrinsic outliner (though I never use this description because extrinsic outliner are no outliners at all but just a tree structure combined with an editor as virtually every filesystem). I was in the same situation in 2008/2009 when I realized that Ecco is no longer scalable, and didn’t find any decent tool, so I wrote my own. I’m not a writer but I author a lot of specifications and I indeed use CrossLine to do this. CrossLine is very practical in this respect because you can use it for interview minutes with all kinds of stakeholders (I actually write everything down they say) and to aggregate the facts from the interviews and finally deduce requirements with (bidirectional) traceability to the aggregated facts and statements from the interview. This also works for internet and literature researches; you can just copy/paste links and add quotes or comments indented to the outline item carrying the link.

Firefox is blocking the download links due to lack of https

That’s strange. On which version/OS are you? If I try on Windows 11 with Firefox 112.02, everything just works fine; if I just click on the link, Firefox shows the download details with a red exclamation mark warning about the security risk, but with an option to continue.

EDIT: you can even just copy the link (context menu), open a new browser window (CTRL+N) and paste the link, then it just downloads without any warnings.

could add them as assets to the release on GitHub instead of external links

Yes, but more work, more redundancy, and especially no download statistics.