Third-party Scripts (Kitten Game add-ons written in JavaScript) allow users to enjoy the game while (for instance) doing less bookkeeping. Some scripts interactively run with and examine the state of the game, others run independent from the game itself.
xpg's scripts - includes:
KG Progress Bars - Scripts that add progress bars.
Save file decoder by coderpatsy
Save Game Editor by KaedeIchigo - updated version of coderpatsy's editor
Public Kittensgame Calculator by zoë: Link to a googlesheets page containing different calculators with uh math and such.
trillian's 1000 years calculator - optimizing when to buy void hoovers/chronocontrols in 1000 years challenges
Some quite old and probably outdated calculators: