The four programs listed below are worth mentioning.When there is no propagation on HF they can help us to get in touch with others.So why to use Skype or something like that if we have such software written by radio amateurs for radio amateurs...
DF1ZN Mike's webpage - software and IOTA program
DX CLUSTER SOFTWARE
MORSE TRAINERS :

LB3KB
ZL1AN
G4FON
VE3NEA
AH0A
DL4MM-IV3XYM
LOGGING SOFTWARE
MODS AND MANUALS
PROPAGATION SOFTWARE AND WINPSK
=====================================================================
=========================================================================