TeamViewer – Because grandma isn't going to help you SSH into her PC, TeamViewer remains a favorite in my household. Available through a specially packaged Wine bundle, TeamViewer works flawlessly across all platforms and even allows the administrator to offer help via their mobile device.
ForeUI – I haven't yet found an open source alternative to ForeUI. Based on my experience, it's the single best prototyping utility I've ever seen for Linux. Brain-dead simple to use, ForeUI allows you to take an idea and generate a fully interactive mockup to demonstrate to others.
Nuke – Linux enthusiasts may not have access to Adobe After Effects, but for those users who fancy themselves to be movie producers, there's always Nuke! Priced for movie creators and not hobbyists, Nuke is a full-featured composting suite that has been used in countless Hollywood productions.
Userful Multiplier – Unlike MultiseatX, you won't spend hours pouring over documentation trying to get it working properly. Userful Multiplier allows you to take a single PC and turn it into multiple virtual desktops. It's a must-have for libraries and schools.
Illumination Software Creator – With the latest release of Illumination Software Creator, there's very little one can't create with a little time and some imagination. To date, there is no other application creator like it that I know of, or that even compares to it. While it's (obviously) not for programmers, it's a great way to take neat ideas for software and turn them into reality.
I realize there are other great applications available, however these are the software titles that strike me as the most compelling. It’s difficult, if not impossible, to locate open source alternatives for these titles.
And while not all of them apply to everyday computing, the specialized nature of their functionality indicates to me that this is software that may never be available with open source alternatives. Hopefully someday I'll be proven wrong on this.
Different software licenses standing together
Many of you are likely to think that I'm suggesting that the proprietary software offered with Linux distributions such as Ubuntu is a good thing. However, I never made that claim. What I will say, however, is regardless of what you or I may think, proprietary software is here to stay on the Linux desktop.
It's a software business model that is tried and true and even though I happen to prefer open source applications whenever possible, I also enjoy the option to buy an application for my Linux PC, should I wish to.
My challenge to each of you is this: before we dismiss the idea of proprietary software on Linux, is there not a single application that you wish you could bring with you from other platforms?
With the sky being the limit, I suspect at least some users have software titles you'd be willing to buy if they were only available.