I'm not up to speed on the current open-source SGF editors, because I mostly use MultiGo or SmartGo, but one feature I've wanted for some time is the ability to extract game variations as problems quickly. For example, starting at a particular move, consider that as the starting board position and all of the variations after it are part of the problem. I'm okay marking the correct variations manually. I think GoWrite2 can almost do this, but it's more designed for printed diagrams and I want something I can use to save SGF for input into other drilling programs like uliGo.

I would consider adding this feature myself to an existing code base, but I'm not going to write an SGF editor just to have that one feature.

So it's some sort of flattening operation? Combine all previous moves into a static board position and preserve all variations that comes after?

You got it.

Hey Calvin, I implemented this feature in the latest version (v0.19.1) of Sabaki. Check it out! You can choose 'Edit' > 'Flatten' or right-click on the corresponding node in the game tree > 'Flatten'.