MedNet – Marine Long Range SSB Radio – for Mediterranean Sailors
https://www.facebook.com/groups/MedNetMarineSSB/

MedNet opens at 0600 UT using 6,516 kHz
= 0700BST = 0800 Central European Time = 0900 Eastern European Time on Mondays to Saturdays (inclusive).
Before closing MedNet will switch frequencies to 8,134 kHz then 12,359 kHz in an attempt to establish communication with others who may be more distant.
MedNet operates during the spring, summer and autumn sailing season. It is not necessary to be a FB member to check-in by radio. The MedNet FB group is, however, essentially for those people using radio communications to have additional means using MedNet FB if wishing to.
N.B. NEW MEMBERS WILL BE REQUIRED TO CHECK-IN TO MEDNET USING HF RADIO BEFORE BEING INVITED TO JOIN THIS FB GROUP

The following 2 informal Nets are not confirmed as still operating:

Local Aegean informal, 4417 kHz at 0800-0900 local time.

Greek/Turkey informal, 6224 kHz at 0500Z, Channel 6A and on 12353 kHz at 0645Z, Channel 12A.

A good source of worldwide SSB Nets can be found here.