The greatest thing about Linux is the vast amoung of free open source software you can find. But that does not mean companies are not allowed to produce commercial software and have Linux as part as their business model too. Have you bought any commercial software for Linux? Is it any good? What is it for? What is their website?
Here is a list for "Commercial" alternatives so far:
Databases
Aqua Data Studio - a Database Query Admin tool similar to MS Enterprise Manager. It runs on Java and is free for personal use. Some limitations concerning MS SQL Server (like editing colums)
Datadino Database Explorer - a Java Database Query and Admin tool. But with a different "lighter" feel. They offer a 30-day free evaluation.
DbVisualizer - another competing Database manager running on Java. They offer a 21-day eval license key. Very rich in features but cumbersome to edit columns (only via scripts)
Development
JBuilder
- A Java Development Platform which is free for personal use.
The personal edition is more limited, but suits anyone who just want to write simple Applets.
Kylix 3 - A Delphi Platform for Linux which is free for GPL projects. The enviroment may be used to develop C++ applications also. It hasn't been maintained or updated since 2002 (probably abandoned?)
Torque Game Engine - A complete cross-platform engine for developing games. The same engine used in Tribes, Starsiege, and Tribes 2. In the site you will find other supporting development tools and some published "indie" games.
Revolution - More of an 'educational' programming language enforcing OO programming. The syntax is pure structured English, and the visual environment is multiplatform. Suse users can get a free copy of Revolution Express. Priced dearly and original made for Mac OS.
Pure Basic - Meant to be the closest you can get to VB 6.0 in Linux. They recently released an IDE for Linux. Anything it compiles they claim runs on Windows/Mac/Amiga. This needs a second test-drive since it runs with GTK and that felt slow on my distro (all GTK apps are slow here). It may be faster on a second distro, will re-test this soon. Or you can test it yourselves
Drivers
Linuxant - A driver that allows some classes of "winmodems" working on Linux. I've recently had experience of this. The installation is not obviously easy, but easy enough. The price is not absurd which at $14.95 ($19.99 now) could see your laptop modem or similar working for ever as a dial-up in case of emergencies. You will need the kernel source installed. You will need to be online (via adsl say) to "authenticate" your driver. It really works and I am impressed but make sure your modem is Conexant based! If you generate a key you will *not* get your money back.
Wireless Driver Loader - From the same company above. They offer a 30-day trial. Well worth it - because in my case it didn't work, but I managed to make the native drivers work instead
ESP Print Pro - Multi platform Printer driver management. The software boasts of over 5300 printer driver. On Linux operates via a webconsole and reconfiguring Cups. They offer a free trial.
http://www.turboprint.de/ - untested
Emulators
Cedega - Provides a way of playing Windows Games on Linux. You can play new titles such as Half-Life 2 or popular titles such as World of WarCraft via their DirectX emulation. Support and downloading of the software works via a minimal subscription of 3 months ($5 per month).
CrossOver Office - The commercial version of Wine. With it you can easily install Internet Explorer 6, Dreamweaver, Photoshop without the hassles of difficult configurations. All works via a friendly interface.
Win4Lin - Allows you to run an almost perfect Windows enviroment. Win4Lin boasts of greater compatibility and speed with Windows applications. As long as they are themselves compatible with the OS you choose to install which is currently limited to Windows 95 / 98 / 98SE or ME.
Netraverse is now offering a
Win4Lin Home edition for 1/3 of the price (well worth it).
Win4Lin Pro - From the same company above.
But meant to emulate Windows XP / 2000. Sadly much more expense though nowhere as fast as Win4Lin. Also not as compatible only some specific SP packs work.
Vmware - Provides a x86 virtual machine emulator whereby you can install most operating systems to work alongside Linux. You will need at last 1 GHz and 512 Mb Ram to take advantage of the software, as its very resource-hungry. Checkout the free download Vmware Plugin.
Graphics, Education & Multimedia
Photogenics
- Photogenics is a Graphics Manipulation Environment that feels very light and very fast Truly responsive. The approach is different - it doesn't resemble neither Photoshop nor Gimp, almost as if the developers sat on a drawing board and re-invited the concept of digital image via an interface from scratch.
Maya - Maya Complete is the only version that runs on Linux sadly they do not offer a free trial, so its difficult for me to tell you about how well or not it performs

[untested]
Main Actor - Video editing software, runs initially only on Suse and Mandrake. But if you manage to get a libavc1394 rpm you will be able to install the trial version which runs for 30 days or your distro - it will add a watermark to any mpeg when you export. Very responsive. The GUI has big chunky visible letters. The software itself seemed to do what its suppose to with many filters and effect for video editing.
QCad [untested]
Studio to Go [untested]
Linux CAD [untested]
http://www.apple.com/shake/ [untested]
http://www.kanzelsberger.com/pixel/ [untested]
Mathematica [untested]
MatLab [untested]
Maple [untested]
http://www.fastrabbitsoftware.com/mathwords.htm [Educational Maths]
http://www.fastrabbitsoftware.com/musicflashcards.htm [Educational Music]
Finances
MoneyDance [untested]
Quasar [untested]
Linux General Ledger [untested]
Games
For a list of all commercial titles try
this
a few titles which are not listed above:
http://www.darwinia.co.uk/
http://puzzlepirates.ubi.com/
DD Poker
War! Age of Imperialism
More Ported Games
- Tux games provide a library of Linux ports most from the
Loki-Software era (2002) now sadly defunct.
From time to time you get fresh releases like Doom3, long awaited ports like Robin Hood, or older rebatched ports like Tribes 2 for a limited time (which rapidly sells out).
Not the best support, so do expect breaking your head and trawling through forums to make their titles work.
Internet
Opera - is free now.
Limewire - Cute File Sharing Applet. And you won't get spyware or trojans. There are two versions to download: free and pro.
Igloo FTP [untested]
Office
Textmaker Very slick, very light WordProcessor that claims to offer better compatibility with Word files than OpenOffice itself. At a price .. that price also includes less features. Very fast on most Linux distros, the launching is almost instantaneous. One month trial free download
Planmaker Following the same trend, this is a Spreadsheet with less functionality than the Titans but very fast. It is sufficiently capable of perfoming most operations. It offers unparallel compatibility with Excel files. One month trial free download.
StarOffice (commercial version of OpenOffice)
Hancom Office [untested]
Primavera (Project management) [untested]
http://www.thinkfree.com/
Utilities
NX [untested]
(add antivirus solutions here)
Skypeout (allows you to make phone calls from your PC) [untested]
Nero Linux (Nero CD burner now for Linux) [untested]
http://www.slickedit.com
http://www.versora.com/products/ [Windows -> Linux migration utilities]