The Advanced Package Tool (APT) has been available for some time now. Debian based Linux distributions used it for several years, but the RedHat Package Manager (rpm) based version is still mostly unknown. It was done by Conectiva S.A., a Brasilian linux distributor. Though developed for their own distribution it works with minor/no modifications with most other distributions (currently tested with SuSE and RedHat).
To be able to use apt, an apt repository is needed. Conectiva users are lucky in this respect as Conectiva provides a public apt repository which can be reached via the internet. Users of other rpm based distributions are less lucky, as they need to provide an apt repository themselves. Here is were apt4rpm jumps in. The apt4rpm package creates an apt repository of an ordinary rpm repository. With other words the apt client software is provided by the apt-rpm project of Conectiva, the server side software is being streamlined by the apt4rpm package. The main application in the latter is aptate which is a contamination of the words apt and update.
A list of public apt repositories can be found at the apt4rpm website.