Features of Mercury

Support for multiple operating systems, you can run the same Mercury version on Mac OS X, FreeBSD, Linux and Windows.

Be online with several MSN addresses at the same time (without starting a new program for every account)
Login with your status on ‘Invisible’ or any other status you want.
Have a different MSN name in every conversation (Personal name)
Send screen shots to your contacts

Add more then 12 users in one conversation (MSN messenger limit)
Special codes in your name.
Nick scroller, change your name every 30 seconds into something complety different (allows the usage of the special codes)

Avatar scroller, automaticly change your avatar every 5 minutes
Background image scroller, automaticly change backgrounds every x minutes
Send larger avatars then normal
Override someones avatar
Enter notes while in a conversation you might need later (date of birth, last name, phone numbers)

See when someone starts a conversation with you before he says something (this has been removed from MSN7, Mercury will now show when someone starts typing, this is the closest I could get to the old function)
See when someone closes the chat conversation window.
See who added you into a conversation with multiple people
See when someone deletes you from their contact list.
See what MSN client version someone is using (or emulating, Mercury currently emulates 7.5)
See if someone in your list is using Mercury
See if someone in your list has a webcam (if he/she allows you to see it)
See your fake, faked and ghost friends

Specific triggers for each person (trigger = action after event)
Supported actions for a trigger include sound, a popup window, a windows balloon (balloon=Windows only), shaking a window
Support for Growl

All avatars downloaded are stored on your computer
All webcam streams are stored on your computer, you can convert them to a Quicktime movie if you want or watch them internally using the webcam stream player
All personal emoticons downloaded are stored on your computer

Text recall.
Auto log chat conversations, always log your chats so you can read back everything that is said between you and your contacts.
Auto login multiple accounts on startup.
Auto away, change your status to away (or anything else) after x seconds of idle time (Windows and Linux only)
Auto update when a new version is available (Mercury asks if you wish to update when new version is available)
XML and text based chat logs

Customize all menu bars.
Customize your contact list:
- Hide offline contacts
- Show emoticons in the list
- Sort contacts by group, status or both
- Show contacts by email, MSN name, alias or a combination of the above, supports multiple lines (List view)
- Change the status icons
- See the difference between contacts using Mercury, contacts having a webcam, fake friends and more
- Show display pictures in the list
Customize your conversation area: (1710 Beta and up)
- By using HTML you can make your conversation looking the way you want it to
- By downloading views other people made, you can find the view you like the most without making it yourself

Show contacts in the program by email, MSN name, alias or a combination of the above (General view)
Add new status icons
Mercury has 10 custom skins and 3 java skins
XML based setting files.

It requires a pretty fast computer if you want to take full advantage of all it’s functions. Since I am using Swing to display the user interface almost no native widgets are used. This can slow things down on older computers.
Not sure if you can call this a downside, but Mercury was not made to be exactly like MSN Messenger. It might take you a few seconds longer to find an option you need. I’m not trying to make a MSN Messenger clone so the user interface is different…