try/catch block with a callback, used in [try-catch-core]. Use it when you don't care about asyncness so much and don't want guarantees. If you care use [try-catch-core].
Low-level package to handle completion and errors of sync or asynchronous functions, using [once] and [dezalgo] libs. Useful for and used in higher-level libs such as [always-done] to handle completion of anything.