Have you considered selenium-sync?

[hackhat]

https://github.com/hackhat/selenium-sync

Features:

• Sync and non blocking using fibers (you can spin your own server from the test);
• Browser/window/element concepts (easy to understand where you are apply a certain change);
• Easy multi window management;
• Easy css selector out of the box;
• Very friendly API docs with types;
• Uses the selenium for JavaScript;