Distributed system tracing:

http://www.erlang.org/doc/man/erlang.html#trace-3

Distributed system profiling:

http://www.erlang.org/doc/man/cprof.html

http://www.erlang.org/doc/man/eprof.html

http://www.erlang.org/doc/man/fprof.html

Nice higher level abstractions of both:

https://github.com/massemanet/eper