Synaptic Package Manager should be a good choice for you to find packages.
To download Synaptic Package Manager, open a terminal and type apt-get install synaptic
with root access.
Another thing is, the default Ubuntu repository does not include all softwares you want, e.g. for Evolution, you have to add the gnome PPA into your apt source list before you can download it.
sudo add-apt-repository ppa:fta/gnome3
sudo apt-get update
sudo apt-get install evolution
This can help you install Evolution in Ubuntu.
You have to manually add the software's PPA before Ubuntu can find the package (and they will never show up in Ubuntu Software Center).
If they do not offer PPAs, possibly you can download a .deb package and install it with dpkg -i
. Or, if they only offer source code, you have to compile it yourself.