An under-appreciated problem with existing debuggers is that they lack first-class support for collaboration. In large projects a debugging session will often cross module boundaries into code the developer doesn't understand, making collaboration extremely valuable, but developers can only collaborate using generic methods such as screen-sharing, physical co-location, copy-and-paste of terminal transcripts, etc. We recognized the importance of collaboration, and Pernosco's cloud architecture makes such features relatively easy to implement, so we built some in.
The most important feature is just that any user can start a debugging session for any recorded execution, given the correct URL (modulo authorization). We increase the power of URL sharing by encoding in the URL the current moment and stack frame, so you can copy your current URL, paste it into chat or email, and whoever clicks on it will jump directly to the moment you were looking at.
The Pernosco notebook takes collaboration to another level. Whenever you take a navigation action in the Pernosco UI, we tentatively record the destination moment in the notebook with a snippet describing how you got there, which you can persist just by clicking on. You can annotate these snippets with arbitrary text, and clicking on a snippet will return to that moment. Many developers already record their progress by taking notes during debugging sessions (I remember using Borland Sidekick for this when I was a kid!); the Pernosco notebook makes this much more convenient. Our users find that the notebook is great for mitigating the "help, I'm lost in a vast information space" problem that affects Pernosco users as well as users of traditional debuggers (sometimes more so in Pernosco, because it enables higher velocity through that space). Of course the notebook persists indefinitely and is shared between all users and sessions for the same recording, so you have a permanent record of what you discovered that your colleagues can also explore and add to.
Our users are discovering that these features unlock new workflows. A developer can explore a bug, recording what they've learned in the code they understand, then upon reaching unknown code forward the debugging session to a more knowledgeable developer for further investigation — or perhaps just to quickly confirm a hypothesis. We find that, perhaps unexpectedly, Pernosco can be most effective at saving the time of your most senior developers because it's so much easier to leverage the debugging work already done by other developers.
Collaboration via Pernosco is beneficial not just to developers but to anyone who can reproduce bugs and upload them to Pernosco. Our users are discovering that if you want a developer to look into a bug you care about, submitting it to Pernosco yourself and sending them a link makes it much more likely they will oblige — if it only takes a minute or two to start poking around, why not?
Extending this idea, Pernosco makes it convenient to separate reproducing a bug from debugging a bug. It's no problem to have QA staff reproduce bugs and submit them to Pernosco, then hand Pernosco URLs to developers for diagnosis. Developers can stop wasting their time trying to replicate the "steps to reproduce" (and often failing!) and staff can focus on what they're good at. I think this could be transformative for many organizations.