OPush stands for Open Push. It is an implementation of the Exchange ActiveSync server protocol. This protocol allows complete synchronisation of the iPhone with groupware servers like BlueMind.

What's in progress / not working

Other implementations of the ActiveSync protocol exists as free software:

• ZPush (I did not use their code as I wanted a Java solution, and most of the libs I needed to use were java ones)

Most other implementations are not free (as in speech and as in beer):

• Scalix ActiveSync
• Zimbra Mobile

If I wanted a non-free implementation, I would pick Exchange.