RADIS was designed for performance: it can compute high temperature spectra with millions of lines in just a few seconds.
Comes with post-processing tools to plot and compare with experimental spectra. Unit support, fitting, instrumental functions, etc.
One-line install, one-line calculation: work in Python, on any OS, with the power of all the Python scientific environment (Numpy, Scipy, Anaconda etc.).
HITRAN support out-of-the-box (auto-download!). RADIS also supports high temperature databases, like HITEMP, CDSD-4000. ExoMol will be next!
Combine spectra to create mixtures of gases or calculate radiative transfer along the line-of-sight.
All the source code is LGPLv3 licensed and available on GitHub.