poGGadaj
Open-source implementation of the Gadu-Gadu server
Patched clients
This is the easiest and recommended way to get started Gadu-Gadu 6.0
The first release of Gadu-Gadu from the 6.x series.
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. 
This client uses a non-cryptographic password hashing algorithm (GG32). A potential attacker can intercept and quickly crack your password. Use a burner password! This client might have compatibility problems under modern OS-es. From my testing this is not the case. 
Gadu-Gadu 6.1
The most popular version of Gadu-Gadu, called by many people "The best version of Gadu-Gadu". At the moment it is the recommended version to connect to poGGadaj.
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. This client uses a non-cryptographic password hashing algorithm (GG32). A potential attacker can intercept and quickly crack your password. Use a burner password! This client might have compatibility problems under modern OS-es. From my testing this is not the case. 
Gadu-Gadu 7.0
The first release of Gadu-Gadu from the 7.x series. The biggest difference is the user interface, as under the hood it isn't much different than 6.x.
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. This client uses a non-cryptographic password hashing algorithm (GG32). A potential attacker can intercept and quickly crack your password. Use a burner password! This client might have compatibility problems under modern OS-es. From my testing this is not the case. 
Gadu-Gadu 7.1
Minor update to GG
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. This client uses a non-cryptographic password hashing algorithm (GG32). A potential attacker can intercept and quickly crack your password. Use a burner password! This client might have compatibility problems under modern OS-es. From my testing this is not the case. 
Unpatched clients
These clients are not patched to connect to poGGadaj by default. Connecting from these clients requires setting the following proxy settings: Proxy IP: poggadaj.ovh Proxy Port: 80 Gadu-Gadu 7.5
Client, which fixes password security and compatibility with newer operating systems
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. 
Gadu-Gadu 7.6
Minor update to GG
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. 
Gadu-Gadu 7.7
This version changed the protocol used for VOIP calls due to license issues. It is the last version before the major 8.0 update. This version is called by many people "The last good version of Gadu-Gadu", and was used for a long time after the 8.0 update.
This client doesn't use SSL encryption, which means that a potential attacker can intercept your messages. Avoid sending anything important with this client. 