Searching through the repository I noticed quite a few extensions with the suffix "rt19". There doesn't appear to be any difference in the info files, other than dates - often the rt19 version being newer.
A google search informed me that rt19 indicated a real-time kernel.
Two questions / comments:
1) Does it matter if the rt19 version is used on the standard kernel?
2) If there is a difference then some information should be prominent in the info file for the extension. If there is no difference when used on a standard (non-rt) kernel, is there a need for both versions in the repository?