Create your own social network, quickly and easily. Elgg allows you to take full advantage of the power of social technology with elegant, flexible solutions for organisations, groups and individuals.

site wide feeds for wpmu

Maatkit makes MySQL easier and safer to manage. It provides simple, predictable ways to do things you cannot otherwise do. It would be nice if these features were included with MySQL, but they are not. That's why Maatkit is now shipping by default with many GNU/Linux distributions such as Debian and CentOS.

Good reference on customizing WordPress RSS feeds.

BackupPC is a high-performance, enterprise-grade system for backing up Linux, WinXX and MacOSX PCs and laptops to a server's disk. BackupPC is highly configurable and easy to install and maintain

A script to take daily, weekly and monthly backups of your MySQL databases using mysqldump. Features – Backup mutiple databases – Single backup file or to a seperate file for each DB – Compress backup files – Backup remote servers – E-mail logs

One question I come across a lot regarding custom fields is how to only retrieve posts based on a custom field.

For example, if a post has a custom field of “MyData”, someone might want to only retrieve that particular post.