Visual Studio Code on Linux now supports debugging of standalone C++ apps:
(You have to do some extra things if you're not on Ubuntu 14.04, the link above explains those steps near the bottom of the page)
Things I've noticed so far:
Fairly usable watch window.
Reasonably speedy so far
Can execute gdb commands within the vs code console with "-exec <the gdb command>"
No way to jump to other threads and see their callstacks in the gui? I see that there are other expandable items listed in the callstacks panel, but when I try to expand any of them, they're empty. "-exec thread <other thread number>" doesn't help either. Weird.
No assembly view that I can see.