I configure postfix to queue all mail, and only send it with "sendmail -q". I run a script that checks the queue, and once all mail in the queue has been there for at least 5 minutes, it sends it along. Of course, I can do it by hand, too.

I end up cancelling an email about once a day, which allows me to go add that missing attachment, fix the CC list, etc. etc.

The projects have different objectives. Scyld builds it clustering by making kernel modifications (it's based on BPROC), so what you end up running is a hacked version of Linux. If this is OK with you, along with the other implications of the Scyld changes, then it's an interesting system. Otherwise, it's not an option.

OSCAR is built in the more classic style of clustering, by building the distribution on top of the kernel. As such, it's an interesting and useful effort.

Scyld and OSCAR are really complimentary efforts. They make different assumptions and take completely different approaches.