The Graz Lagrangian (GRAL) system is a Lagrangian particle model with a free Graphic User Interface (GUI) available in both Linux and Windows. The last beta was published last November and now the developers have released the version 20.01. The software is now open source under a GPL-3.0 license, so everybody is welcomed to contribute to the project. The source code, has been published in github.
The Graz Lagrangian Model - GRAL - was initially developed in 1999, and has been used extensively in regulatory assessments and scientific studies. The initial driver for the development of GRAL was the need for a model that could deal with the frequent low-wind-speed conditions (< 1.5 m s-1 for up to 90 per cent of the time) in the inner-Alpine basins of Austria. According to the developers, there are around 600 users worldwide using, the GRAL/GRAMM system.