Remote access is very useful if you are good in computers and your friend needs your help but he is at another location. Just ask him to launch the remote access application, give you some info generated by that application on his computer, and voila, you can connect to his desktop and help him to solve his computer problems remotely!
Not as powerful as the pro version, but at least it supports voice. The other two software do not have voice support.
For TeamViewer, the main selling point is that the person requesting for remote access or help from you do not have to install anything on his computer. He/she just needs to download and run an executable file either for Windows or Mac version. The app will generate the code and once he/she gives you that code, that app can be deleted from the his/her computer.
Another good feature of this app is that it has a portable version for Windows machine. So you can just download it into your flash drive and bring it wherever you go. Unfortunately, no portable version for Mac yet.
CrossLoop has just recently introduced the Mac version. As with TeamViewer, you don't have to register to use this software.
Happy remote accessing!