Local RPM Files
Some vendors offer their app as a .rpm download. Install it with rum, or double-click it to open it in the Software Center:
sudo rum install ./some-app-1.0.x86_64.rpm
RakuOS keeps a copy of the file in /var/lib/rakuos/local-rpms/ so it can reinstall it later if needed.
If the app won't start afterwards
rum installs a downloaded .rpm exactly as it is, without installing the other packages it needs. If the app then fails with a message about a missing library (error while loading shared libraries: libfoo.so.1), find the package that provides it and install that:
rum provides 'libfoo.so.1()(64bit)' # which package has it
sudo rum install <that-package>
If the vendor offers a repository instead of a single file, adding the repository is usually better: updates then arrive with your normal updates. See Repositories.