Basically, it looks like it's going to be Opera on the Chrome engine, but with the return all the cool unique features Opera ditched when they switched engines a little while back. And hopefully managed by a group that has the spirit from Opera's good old days.

What about Otter Browser?

http://otter-browser.org/

I tried this a while back (a few months?), and it doesn't seem like it has progressed much. I think Vivaldi has a much better chance of getting somewhere. A bunch of coders doing work on a voluntary basis will have a hard time competing with teams of full-time paid engineers.

I'm surprised I haven't heard of this until now, it's made by a group of members from the now closed Opera (12) forums. There are people who are fond of the Presto version's features so I'm glad there are efforts like it.

As an old fan of Opera I'm starting to like v27. Sure I can't use it for torrents or mail, but the new bookmarks are neat.

Most of the UI is based on React. But we use a lot of open source projects. If you run it you should visit vivaldi://credits

It's cool that you use a lot of open source projects. But some of them are under licenses that require the user to be able to download their source code, and it's not obvious right now where (for instance) your Webkit code is. You should probably fix that.

And as an aside - if you're linking LGPLed material into a static binary (as you appear to be doing with Webkit), you need to follow the provisions of section 6(a) of LGPL 2.1 and provide object files that allow the recipient to re-link the binary with a modified copy of the LGPLed work.

According to that, it seems that Vivaldi uses a lot of GPL'd and LGPL'd libraries, and it's not clear that Vivaldi is in compliance with the copyleft requirements of those licenses, nor is it apparent which license Vivaldi is released under as well (be it a FOSS license, some EULA, etc.).

There are also a lot of libraries listed that are licensed under the Mozilla Public License, which is incompatible with the GNU GPL. Distributing this therefore might not actually be legal, regardless of whether or not it's released under a FOSS license, since those two license families have conflicting requirements for derived works (including works which use those libraries).

YMMV, IANAL, etc., but this thing's running the risk of legal technicalities killing it in the crib.

Please just give us a native window that works like the rest of the application windows on my OS though. What's the need for customizing the UI so that it doesn't fit in with the OS?

Since it seems to use atom-shell for the UI[1], it's likely Chromium.

[1]: https://vivaldi.com/#Features/4

User agent provides further evidence, mine reports to be Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.89 Vivaldi/1.0.83.38 Safari/537.36

Provided it is not open-source, it can repeat the fate of Opera Presto one day...

Yes, Otter Browser is a safer bet as it's free software.

yes the web site really fails at two of the things I am interested in: what engine does it use and what does it look like.

Someone should bring this to Windows...