Free - Remote Desktop Control Software

To sum it up: 

For business, Use LogMeIn for unattended, Join.me for attended.

For personal: Use TeamViewer.

The first and highest rated product in the unattended category is LogMeIn. This is a web-based service that's extremely easy to set up and use and can be accessed from any PC with a browser. The free version won't allow file transfer or remote printing but is a great solution for accessing your remote data as well as file sharing. Registration is required before using the product. It is really meant to be an 'install and leave it' kind of tool and not for the 'quick connect to help a friend' scenario. I still very much believe that the features and speed of LogMeIn are unmet by any other product and worth the extra hassle if you have access to the other machine(s) or means to connect remotely and install it. It is free for personal and commercial use.

Next is TeamViewer. It is very reliable, allows both attended and unattended control and has great features. There is a portable version of the viewer if you want to use an application or they also have a web-based control site that requires no installation to remotely control computers. The web-based version uses HTML and Flash, so it is usable even if the browser or firewall doesn't allow Java or ActiveX. TeamViewer is a commercial product and is only free  for personal use. Any commercial use is prohibited by the TeamViewer use policy.

The fastest solution in the attended category is Join.me. Its small 1 MB download and simple security code make it very quick to establish a remote session.

The last solution in this category is Mikogo. Mikogo is not the fastest nor is it the most reliable, but it offers the most features of any of the solutions in this article. It is a full-featured solution comparable to the commercial Citrix GotoMeeting product with features such as presenter switching, remote control, white board sharing, file sharing and session recording.

Source: http://www.techsupportalert.com/best-free-remote-access-software.htm