Maybe it's just that I haven't used it enough, but whenever I have some pentestish need and reach for Burp I get disappointed. The UI is confusing and everything is just so cumbersome, seemingly without reason. I get vibes of old school blender (with the right-click to select behaviour).
I would pay good money for something in the style of Proxyman, with Burp Collaborator features and a sensible extension system.
Perhaps the only contender to Burp in respect to functionality/features is ZAP[2].
EDIT: You can run your own collaborator type setup with Project discovery's interactsh[3].
Further EDIT: A downvote might be because of the mention of Rust / closed source - this is explicitly mentioned because a large pain point for Burp is it's a Java memory hog. If Caido was written in C++ with Qt, this fact would be notable for the exact same reason.
We are not open source since we are a small bootstrap shop and sales drive our growth. I have nothing against OSS but it is not a business model.
We are client/server at heart, you can run the server anywhere and access it via the browser.