Tempo2 is a pulsar timing package developed to be used both for general pulsar timing applications and also for pulsar timing array research in which data-sets from multiple pulsars need to be processed simultaneously. It was initially developed by George Hobbs and Russell Edwards as part of the Parkes Pulsar Timing Array project. Tempo2 is based on the original Tempo (ascl:1509.002) code and can be used (from the command-line) in a similar fashion. It is very versatile and can be extended by plugins.
https://ui.adsabs.harvard.edu/abs/2006MNRAS.369..655H, or https://ui.adsabs.harvard.edu/abs/2006MNRAS.372.1549E when discussing the timing model.