Neither Binding.of_caller nor ruby-breakpoint/Rails' breakpointer work
anymore with Ruby 1.8.5.

call_stack contains a new Binding.of_caller implementation that works with
Ruby 1.8.5, allowing you to use ruby-breakpoint and Rails' breakpointer.

http://eigenclass.org/hiki.rb?call_stack+0.1.0

call_stack can be also be used to obtain backtrace information in a running
program.