[sudosysgen]

Limits are conceptually equivalent to infinitesimals. Another way to view it is that a limit is a way to evaluate an equation of infinitesimals.

Epsilon Delta is not our definition of limits, it's the definition of the derivative that uses limits as the "backend". But even using infinitesimals you can use the epsilon-delta definition of the derivative.

[east2west]

Perhaps you are referring to modern nonstandard analysis, which I am sure has equivalent definition of limits. I will note that in standard calculus Epsilon-Delta is not only used in defining derivatives, but also used in defining function limits, which of course means used in defining integrals.

Just out of curiosity, in nonstandard analysis is there an equivalent of Lebesgue integral?

[mjreacher]

There is indeed an equivalent of the Lebesgue integral available in several textbooks, for example `Nonstandard Analysis for the Working Mathematician`.