Q: Is there a Zip file with all the addins in? Why don't you create one?
No. It could never be complete because several addin developers request that their addins are downloaded from their own websites and I respect their preference. This means that users will always have access to the latest update they have done and allows the developer to monitor the downloads of their addin.

Q: I've downloaded an addin and installed it on the rex but it appeared as a memo file?
You probably downloaded the file with Netscape 4.x. This has a problem with downloading raw .rex files and corrupts them. The rex checks the format of the files that are sent to it and only puts it in as an addin if it has the correct format, if not it assumes it is a memo file. The easiest solution is to use a difference browser for the download.