SKYPE is probably the most popular free tool that many use to have simple web conferences with their family, loved ones and even with colleagues / partners at work. There is also a portable version that installs into a thumbdrive or external hard drive. This made Skype fully portable and you don't have to install it into your computers. However, if you are using a office locked-down computer, you may want to test that Skype can run on that computer from your thumbdrive first. The security policies on the computer may block certain ports that Skype needs to use. Similarly, some offices have firewalls within the office network that blocks some of the ports that Skype uses. Thus you may find it impossible to have Skype to connect successfully in your office in such cases.

Here is the link where you can download a portable copy of SKYPE:

http://portableapps.com/apps/internet/skype_portable