The best replacement for callbacks is closures.

The best alternatives to callbacks are rated as following:
★★★★★  closures
★★★★★  events
★★★★  promises
★★★  coroutines
★★★  polling
★★  events c#
★★  signals and slots
★  observers
★  call backs

Your alternative for callbacks is not listed? Suggest!
Speaking about callbacks, one probably shouldn't forget about javascript.

Other search terms related to callbacks and their ratings are:
★★★★★ javascript
You have in mind a companion for callbacks and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of callbacks in all years. Click on graph for more.
callbacks
closures
events