CHIRP is a free, open-source tool for programming frequencies and settings into your amateur radio. It supports a large number of make and models.
It is really easy to use and makes it extremely simple to copy frequencies between different radios (of different makes). Not all radios are supported by CHIRP however, so it's a good idea to make sure CHIRP can program a specific radio before buying it.
See the Radio Programming page to download VA7FI's Chirp list.
Baofeng radios can be a bit tricky to program with CHRIP the first time around because of the Windows Driver. If you're trying to use CHIRP on Windows with a Baofeng radio, see this page first.
Now that the appropriate drivers are installed:
sudo usermod -aG dialout YOURUSERNAME