It's Mint's alternative to usb creator. It is a graphical application to write .img and .iso files to USB keys. It can also format USB Key from a contextual menu in Cinammon and KDE desktops. It can be used in other linux systems, at least in Ubuntu for sure.
sudo add-apt-repository ppa:tsvetko.tsvetkov/trusty-backports
sudo apt-get update
sudo apt-get install mintstick
UPDATE: that ppa is not updated and will not work in latest Ubuntu 18.04
For Ubuntu 18.04, until a newer version is launched along with a Ubuntu 18.04-based Linux Mint, download latest version 1.3.8 from here.
Open a terminal at the location of the download and do
sudo dpkg -i mintstick_1.3.8_all.deb
Install the missing dependencies.
If needed do
sudo apt --fix-broken install
then do again
sudo dpkg -i mintstick_1.3.8_all.deb.
Actually mintstick is an improved version of USB-ImageWriter, which is based on dd utility and came from OpenSUSE and can work with any distro image. But Startup Disk Creator (usb-creator) is made for ubuntu and ubuntu-based systems only. It also has optional persistence option (all changes made to the system are saved, unlike a Live CD) which minstick doesn't have.
mintstick, you will then have both the Image Writer and the USB Formatter.