strace is a system call tracer, i.e. a debugging tool which prints out a trace of all the system calls made by a another process/program.
KGDB is a source level debugger for Linux kernel. It is used along with gdb to debug Linux kernel. Using KGDB, kernel developers can debug a kernel similar to application programs. KGDB is a kernel patch. It is available for i386, x86_64, ppc and s390 architectures.
Gcov is a test coverage tool. You can use it with GNU CC to analyze your programs in order to make the programs more efficient. You can use gcov as a profiling tool.
Dprobes is the short for Dynamic Probes. As a Linux debugging facility, Dprobe will operate under the most extreme software conditions. By the technique of debugging in both kernel and user space, the users are able to insert "probes" in running programs.