FLARM is definitely not a poor mans version of TCAS. They use different technologies and fulfill different purposes. TCAS is designed for IFR only, i.e. warns you when the ATC IFR separation minima have been, or are about to be, deceeded. TCAS cannot practically be used for VFR, since it would give you lots of annoying warnings (especially close to aerodromes, where most accidents happen). FLARM on the other hand is especially designed for VFR. It uses precise GPS positioning and flight path and collision algorithms, which would not be possible with the limited accuracy of TCAS (which is fine for IFR though).