We have already posted some portable softwares
Miranda IM is a multi protocol IM client which supports ICQ, AIM, MSN, Jabber, Yahoo, IRC and more. This is a Windows app.
Newspeak is Newspeak Cocoa IRC client for Mac OS X.
Gaim works with MSN, AOL, ICQ, Yahoo, IRC and many other networks.
This is an instant messaging client package and supports AOL, Yahoo, MSN, ICQ networks.
aMSN Instant Messenger
aMSN is a free MSN portable messenger.
Emesene is a free MSN portable client, or MSN Messenger Clone.
This is a cross platform IM service which works with Linux, Mac or Windows.
This is a free portable Voip Over IP application.
This is a standalone voice conferencing application containing both a client and a server.
This is a Skype Portable Launcher which can convert an existing installed Skype software of your PC to a portable Skype.
This is a portable version of Skype chat application, which works for free instant messaging, video chat and phone calls. Skype Portable available for Windows OS.
Koma-Mail is an email client works for Windows OS.
The Quick Mailer
This program works for sending quick e-mail messages without having to load your main email client program. The Quick Mailer works with all Windows OS.
gDisk is a software that turns your GMail account into a portable hard drive. This is a Mac OS X application.
Pop Peeper is a free Email client works with Outlook Express, Windows Mail, GMail, Hotmail, LiveMail, MSN, Yahoo, GMail, Mail, MyWay, Excite, iWon, Lycos, RediffMail, Juno and NetZero accounts.
This is a text only Email client. It can handle attachments, but does not render HTML emails or display images within email message.
Share with us in comments below, if you know another portable application.