While there's plenty of software available out of the box for Ubuntu (and all the derivatives), some developers only provide .deb downloads from their websites - that's where deb-get comes in.
The idea is that it sources various extra applications for you, giving apt-get like functionality for 3rd party repositories or via direct download. Sounds pretty neat! A nice time-saving tool developed by Martin Wimpress, lead on Ubuntu MATE. It could help when you're getting setup initially, or just looking for something that isn't available from Ubuntu directly or Ubuntu perhaps has an older version than what you want to install.
Wimpress said the idea is directly inspired by Software Boutique, a tool used on Ubuntu MATE that does very much the same thing with a curated selection.
There's quite a lot of software already supported so go give it a whirl and see what you think.
Check it out on GitHub.