The motivation for this project stemmed from the observation that Chromium and other layout engines have become suboptimal for use in desktop app UI due to a separate set of design goals (running untrusted code, favoring performance at the cost of memory, the need to support every web platform feature under the sun, etc.).
Most native apps also need finer control over low-level platform functionality (such as file system, rendering, clipboard, etc.). Ultralight aims to not just be lightweight, but to offer native app developers much deeper integration with the underlying HTML engine.
Ultralight is also pure-GPU, meaning that all rendering (text, shadows, images, CSS transforms), is done via the GPU. The renderer emits abstract GPU commands (see the GPUDriver interface) which can then be handled by whichever graphics API you prefer (we provide stock implementations for D3D11, OpenGL, and Metal as of this writing).
On top of Ultralight, we've built an additional layer called AppCore that handles window creation, native event loops, native graphics API drivers, and more.
AppCore is intended to be used by those intending to build a standalone HTML-based desktop app and will eventually offer an API similar to Electron.