The latest version of RPM (4.10) that was recently released supports dpkg-style tildes (~) in version/release strings.
The tilde character can be used to append a label such as “beta” to a package without actually incrementing the version of the package. For example – package-1.0~beta. In this case, the package package-1.0~beta would not replace package-1.0 as the former package is considered to be an older version, even if it was released later.
See here for more information.