Is there any IDE/GUI support for git-flow on Windows/Linux?
AFAIK there is no GUI that support git-flow.I develop in Eclipse but use 3rd party GUI's and CLI for git.I too use git-flow, I actually use my own fork with bug fixes and enhancements, and use it from the CLI.I use git GUI for committing, as for a while I used submodules and egit doesn't support that yet and I use gitk for checking my history.And then I use egit when I quickly want to change branches and.or tags.
You can add commands in git gui, maybe something worth to check out.