XNet is a thermonuclear reaction network for astrophysical applications, using a variety of temporal integration techniques. It is written in portable FORTRAN 90 and makes use of a variety of matrix solving packages to obtain excellent speed (as much as 50% of peak) on as many platforms as possible.
The version contained in the repository is targeted at standalone execution (post-processing nucleosynthesis). However, with the appropriate interfaces, XNet has been used in a variety of large scale simulation packages, including FLASH, CHIMERA and several other codes.
Before you dig deep into the source code, we suggest you learn the basics of how thermonuclear reaction networks function, from one of the following sources.
"Thermonuclear Reaction Networks for Astrophysics" by Raph Hix, http://astro.phys.utk.edu/_media/gallery:networks.pdf
Tools and Toys for Nuclear Astrophysics: Nuclear Reaction Network Techniques by Frank Timmes, http://cococubed.asu.edu/talk_pages/jina.shtml
Thermonuclear Kinetics in Astrophysics by Raph Hix and Brad Meyer http://dx.doi.org/10.1016/j.nuclphysa.2004.10.009
Supernovae and Nucleosynthesis: An Investigation of the History of Matter, from the Big Bang to the Present by Dave Arnett http://press.princeton.edu/titles/5859.html
Someday, we'll make a list of publications using XNet, but that will wait...