ptrace is the kernel support for debuggers like gdb, and has existed for decades.
kprobes/utrace/dynamic probes are names for difference parts of the various tracing systems people are writing; if you just want to know when we'll get DTrace then you don't care about their details. (DTrace has a bunch of comparable internal pieces too, of course.)
SystemTap is an end-user product that attempts to provide approximately the same capabilities as DTrace.
DTrace doesn't exist on Linux because it fit Sun's strategic goals to keep it as a differentiator between Linux and Solaris, and they licensed it accordingly. Oracle has different strategic interests, so it'll be interesting to see if they have a different take on this.