List of open-source "stuff" that every web developer should know about.

Question

These are some of the things that every web developer should know when building a web app. This tools will save everyone lots of time. Tools like "memcached" and "beanstalkd" are super dead simple and provides lots of value. If someone could list their simple yet effective tools in this list, it would be good.

I'll make this community wiki, and people can add on to it. If possible, someone should group this by function (database, framework, sysadmin) rather than importance.

Essential:

1. Apache - web server
2. Memcached - Dead simple key/value memory caching
3. Scribe - Logging and statistics
4. MySQL/PgSQL-database
5. Sqlite - very simple database for light stuffs - if you know 4, this is trivial
6. Cacti - use this to trace network stuff - sysadmin

Web Developer

1. Firebug - for javascript tracing - XMLHttpRequests
2. "Web Developer" addon for Firefox - Templates/CSS/form information

Somewhat Essential:

1. Facebook Cassandra - What is it?
2. Beanstalkd - Dead simple Queue
3. PerlBal - Dead simple software load balancing
4. Sphinx and Lucene - Allows you to build a search your data/indexing

Answer 1

Hibernate the ORM

Answer 2

Some version control system (Subversion, Git, Mercurial...)

Prototype/jQuery/Mootools library.

Answer 3

Some of the popular PHP frameworks:

Zend Framework

Cake

Code Igniter

APIs to get familiar with:

Google

Amazon

Yahoo!

Flickr

And of course, programmable web

Ajax/Cool Stuff

jQuery

Yahoo YUI Library

Interface for jQuery

Rich Internet Platforms:

OpenLazlo

Adobe RIA

Sproutcore