I’ve started a plugin that implements some useful base widgets and a simple menu manager to create game user interfaces in Unreal Engine 4. It’s sort of a spiritual successor to the SharedXNA library used in most of my XNA games.
It’s open source under the zlib license, mirrored to GitHub at https://github.com/joat/SharedJamUI. There’s a bit of usage information in README.md, but it’s pretty early and should be considered ‘jam quality’ code that hasn’t been really battle tested yet. Drop me a line if you end up using it and have some feedback.