With Thanksgiving upon us, let\u2019s look at some of the open source tools and applications for which Linux pros are most thankful.The following rundown is based on various surveys I\u2019ve come across, reader responses to this newsletter, and conversations overheard in computer rooms, network closets, and in front of the candy machine:MySQLThe king of open source databases, readers have told me over and over how valuable this platform is for building Web-enabled databases, back-end databases for corporate applications, and as a test database environment for software development.PhpMyAdminFor managing all those MySQL databases, users apparently love this free open source tool. Written in PHP, this decade-old program lets users administer MySQL databases remotely over the Web. It\u2019s one of the top downloads among IT-focused open source software tools on sourceforge.com. And many of the same newsletter readers who have expressed their affinity for MySQL have written saying this tool is almost as critical to them as the database itself.CrossOver PluginFast becoming a standard on many commercial Linux desktops, this tool - made by CodeWeavers - allows Microsoft applications to run as native applications. Built on WINE, the well-known Windows emulator for Unix (oh, sorry: WINE Is Not an Emulator!), the CrossOver Plugin family includes versions for Microsoft Office and Outlook, allowing users to keep running these often-mandatory corporate applications in a more secure Linux environment.\u00a0Mozilla FirefoxThe most popular open source browser with Linux users, (and second only to Internet Explorer overall), Firefox doesn\u2019t need much of an introduction. Tabbed browsing, enhanced security, and hacker-friendly plug-in architecture have helped contribute to over 100 million downloads and 7% of the browser market.EtherealThis protocol analysis tool is used to troubleshoot networks by capturing mirrored streams of network traffic, digging into the network transport layer - ATM, Ethernet, FDDI, PPP, Token ring and 802.11 wireless among them - and analyzing the behavior of more than 724 protocols, from TCP to DEC DNA and MPLS. This is the favorite tool among many of Network World\u2019s test experts, too.Apache ToolboxApache Web server is legendary, but every try to compile it? Users swear by this tool, which allows Apache source to be easily compiled with a variety of add-ons and features, such as SSL, MySQL, IPv6, Java, OpenLDAP, and other open software. Not having to download the honkin\u2019 80M-byte Apache tar ball, the menu-based interface and error-checking features are reasons for this tool\u2019s popularity.Of course this does not scratch the surface by a millimeter in terms of what open source and Linux IT tools are out there. I\u2019m always interested to hear what people are using and why.