strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
ftrace - A function tracer for the Linux kernel.
Snare - Snare is well known historically as a leader in the event log space.
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.
Kafka - Apache Kafka is publish-subscribe messaging rethought as a distributed commit log.