JPALME  REALBasic is a general purpose programming language.

Pros:

+ Available for Macintosh, Windows and Linxu including cross-compilers between hosts.

+ Has everything you need, and more. For example, I needed to write software to communicate with the Internet, using HTTP. This is rather difficult to get right, since HTTP allows partially downloaded documents to be usable before everything has arrived. I first tried to write this from scratch, and did not get it working. Then I noted that a HTTP package was already available in REALBasic, and got my program running at no time. This is just one example of what is available when you need it.

+ Good on-line debugger.

+ Easy to get new applications running.

+ A compiler, compiling into source code, not only an interpreter like many other modern programming languages. This makes code efficient for complex, time-onsuming applications.

+ Full built-in support for the Unicode character set. My advise for new applications is to use Unicode only, If you get input data in other character sets, thn convert into Unicode as soon as you get it. If you really need other character set, support is available for many other character sets, like ISO Latin 1.

+ Good built-in support for databases using SQLite or other data base systems.

+ Good support for building simple user interfaces, including text editing in text boxes. You can build a new simple text editor in an hour or less.

Cons:

+Text string handling somewhat inefficient because you cannot modify text strings without copying them.

+ I lack a set of very simple program templates, like "copy text file, modify it, output as a new text file" or "Copy all files in a folder and produces modified versions in a new folder".   
(Version 2009.5.0.0)

QBAP  REALbasic is a easy to learn cross-platform programming language. It offers everything you need to make nice applications for Linux, Mac or Windows. But there was always a problem with getting the knowledge about this language. Now after years arose a great learning resource for REALbasic - http://realbasic.tutspolis.com/  
(Version R4)

CANTLON  People should be aware that RealBasic is *not* backwards compatible--if you write a program in RealBasic, it won't even open in the version they put out 5 years from now. My library of hundreds of RealBasic programs (that were written between 2001 and 2005) is totally useless now because none of them will open in the 2008 and 2009 versions (I've talked to RealBasic staff about this and they claim that this phenomenon is totally normal...sure it is).  
(Version R4)

RUBAIYAT  Well here we are well into the 3rd quarter of 2009 and still waiting on Cocoa support.  
(Version R3)

GREGORGY  Eagerly awaiting Cocoa support...

It is coming mid-year, according to reports from the Real Software but I gotta say, that is a bit late.  
(Version R1)

A FLOCK OF BUDGIES  I have been a REALbasic user since version 1.0, so I am familiar with all the improvements REAL Software has made to this product. REALbasic just keeps on getting better and better with successive releases.

Next year, I am really looking forward to being able to use Cocoa objects with REALbasic code - that is going to be so cool IMO.

Keep it up REAL Software! REALbasic blows Visual Basic out of the water!  
(Version R4)

EGN  I come from the web-app programming world.

Had been looking for a good, solid development platform for Mac. Tried Xcode, read Hillegrass (Cocoa programming for Mac OS X-3rd edition), but man, Objective C is not my cuppa! And, I could only develop for the Mac using these (maybe porting and jumping through fire hoops could ge my apps on other OSs). Also tried Runtime Rev. but found that to have an inconsistent interface, very un-Mac-like, almost Java-ish, and with a language that although is almost like spoken English, is very hard to remember. And the "stacks" deal... Tried a couple more and those were worse.

Then I found RealBasic. The interfase is consistent (and as Mac-like as can be), the documentation adequate and the learning curve much, much flatter than Xcode/Objective C or other competitors. You do all your coding from a single window, even creating databases and tables.

Plus, you can code once and use the apps you create in three different operating systems (if you use the Pro version; personal is just for the OS you are on; on Linux, RB is free!).

With RB you can program using OOP or from the top-down. I have not had it for long but it looks like I'll keep this one.  
(Version R3.1)

JEFF HENDRICKSON  I've been using REALbasic since version 5.4. It bothers me sometimes when I see it described as a "hobbyist's" tool. I use the pro version of this excellent development tool exclusively to develop my cross-platform commercial software products, including "Purify."

REALbasic offers a lot, and like anything else, you need to dig into it to discover its true capabilities. Technical support is great, and responsive. The online support community is great. The product has everything that you need to do real cross-platform product development. The only plugin that I've ever needed is the MySQL plugin for some of my Linux server based apps, which by the way works great. My primary development environment is OS X 10.4.11, on a dual PowerPC Mac with 1.5GB of RAM and a Cinema Display, and REALbasic is a pleasure to use in this environment.

My recommendation, if you're looking for a powerful cross-platform development tool, look no further than REALbasic Pro.  
(Version R2)

SHOTGUNWEDDINGS  I love all the negative feed back from the nay sayers. The clueless never cease with their tripe.

RealBasic is fun to program with once you get the knack of it.

Its easier to learn and so what if a few bugs are in it still, very few programs are bug free these days.

Why spend months or years learning programming languages when you can create your own programs with RealBasic within hours!

Try the demo version and see if it works for your needs, what can you lose.  
(Version R2)

ALEKSI STRANDBERG  REALbasic does take more memory than well designed C programs.

Now all Macs ship with 1GB of RAM

REALbasic does take more CPU time than well designed C programs.

Most user's CPU's are more or less idle all the time.

REALbasic does create bigger files than Xcode.

Most people nowdays have a fast DSL connection.

The most affordable MacBook comes with a 120GB hard drive.

With C/C++ the programmer's own resources are very much occupied.

There is a huge amount of information to remember and take care of.

With REALbasic, the user can use these spared resources in other areas.

You can't write a game like WOW with REALbasic, as such thing would require the absolutely optimal use of the computer, but this doesn't mean that you are limited to just writing stuff like database apps with REALbasic.

Features which are now crucial for me were just included a year ago.

And they are still developing it.

When it comes to bugs, in my own experience, the apps I have used extensively, they all have more or less bugs, except Reason.

Paying for bug fix releases?

REAL software is not a big company.

Usually the same code works for both Mac and Windows, which is just amazing.

REALbasic and C++ can work together too, you can hook your REALbasic application to C++ libraries easily.

The IDE itself is slow to operate.

How fast can you really write?

Isn't that what most of the work is about?

It is a Rapid Environment and you can accomplish good results with significantly smaller development teams and/or timelines.  
(Version R1)