Rotala is a backend backtesting library/application built with Rust. You can run Rotala as a standalone server or import the exchange in Rust. Alator is an example implementation of the latter approach.
Alator started out as a backtesting library used in another application. Over time it became clear that backtesting was a standalone application, and then it moved towards developing something cross-language that could run on a server. This transition is still at an early stage and this isn't a production application.