What contributions did Solon and Calisthenics make to the development of the Athenian democracy?

Solon was not interested in democracy - he was given the task in Athens of settling dangerous disputes between the upper class and the farming class being exploited by them, and produced a compromise which averted revolution, but it was not democratic.

The beginning of democracy came over 80 years later in 507 BC Ewhen Cleisthenes introduced an assembly of the propertied class. This launched democracy, but the aristocrats took over again during the emergency of the Persian wars, and democracy was not re-entrenched until 461 BCE when Ephialtes re-established the popular assembly and sidelined the aristocracy. His deputy Pericles took over and took it further when the aristocracy assassinated Ephialtes.