Unagi is a modular compositing manager which aims to be efficient, lightweight and responsive. It is currently written in C programming language and based on XCB library client library. Any existing window manager can be used as long as it implements properly EWMH and ICCCM specifications (or at least parts of it which are needed), which is generally the case nowadays.
This project also aims to provide a functional and stable software to improve window manager usability from an end-user point of view (for instance windows translucency, application-switcher using live thumbnails instead of plain icons, Exposé...), therefore it does not intend at all to provide useless eye-candy effects.
A compositing manager is a piece of software running along with the window manager and where each graphical program outputs into a separate and independent off-screen buffer that can be manipulated before being shown in order to enhance user experience. Unlike a compositing window manager such as Compiz, a compositing manager does not manage windows but simply implements visual effects such as windows translucency, drop shadows, fading... Therefore, it is generally used along a window manager.
Unagi relies on a modular architecture as the code is split up in three parts: core code, rendering backends (only one backend relying on
Render X extension has been implemented so far) and effect plugins. Thus, it provides a small and fast compositing manager from a codebase and footprint point of view, besides allowing to easily write other rendering backend which would work better on certain hardware. It also tries to take advantage of the asynchronous XCB model to be able to be used through a network.
Further documentations are available on Wiki.