Not all distributions use RPM to manage software packages. Distributions based on the Debian distribution use the Debian Package Manager (dpkg) instead. Ubuntu is probably one of the most popular Debian-based distributions that uses dpkg instead of RPM to manage software. Debian packages are similar to RPMs in functionality but are totally different in the way they are implemented.
NOTE Occasionally, I encounter folks who mistakenly think RPM and Debian packages are cross-platform compatible. They are not. You can only install RPM packages on RPM-based systems and Debian packages on Debian-based systems.