@2e71828 Conrod does not provide child windows(reposition, expand, contract, resize) within the main window, and if it did, I would definitely stick with the piston ecosystem since I like its modularity.
There are many apps that have the game + GUI widgets requirement; especially, for example, an online chess interface app which needs simple 2D animation in main window with several child windows with scrolling for event and other chess-related feedback.
It's also convenient to move and reshape the child windows as needed, or have multiple chess board window displays during analysis.
There are other ongoing Rust-based multiplat toolkits under development such as OrbTk, ezgui, and Iced, but they are not 100% ready yet. There's also an effective offering of imgui + ggez that also nicely covers how to use them in tandem with the ECS paradigm.
Requirements can be met with Rust, but my selection of piston has been disappointing. I'm certain things will improve with time!