I've actually had occasion to make RAD-style tools in the far-flung past. This is the sort of platform I would have made if I could.
Some of the initial steps are a little harder than you would expect, but once you are used to where everything lives, it's easy to find it again.
Coding is done via flowcharts, and these are pretty easy to use, not to mention fairly easy to use straight up as diagrams to show other people what's going on.
OutSystems is pretty good for only showing you matching options, e.g. if you need a date, it will show you everything local with a date and important functions, like the current date. If you adopt certain naming conventions, OutSystems will fill in the type for you: IsSuccess will become Boolean on account of the "Is" part. JobEntryId will become a Job Entry Identifier.
Database design is extremely easy, just add, adjust and publish in a tree or diagram and migrations are automatic, though when you remove things, it won't remove them from the database automatically.
Using the databases is even easier. Drag and drop the columns, join whatever is not automatically joined, add sorting and filters and OutSystems will try to choose a sample of your data. This sample can be changed by changing the test value, e.g. let's see UserId = worker1.
There's a "business processes" that looks strongly inspired by BPMN 2.0, though it is not identical. These can be used for long-term states or even just simple asynchronous programming.
The web interface side of things is pretty slick, though it can be quite ornery about exact placement. I would recommend using the widget tree view instead when this happens to avoid frustration. There is some pretty good support for Responsive Web Design, especially if you choose a theme designed to show on many devices.
If you are missing some functionality, one option that is available is to make extensions. I've made a few of these. The programming side is a bit esoteric , and there are some odd holes (can use a list of records but not a list) but it's pretty good once you get the hang of it.
A few complaints or improvement opportunities: it would be nice if it was a bit more object-oriented. Built-in tools for data migration, especially between Development, Testing and Production, would be most welcome. I also found myself desperately wishing for a try...finally construct. Java versions of components are a bit neglected.
It's been very, very productive all said.
The hard things made easy - the BPMN capability, the tree editing and republishing of data entities, the Responsive Web design. Also, the fairly intelligent guessing about properties, the rather speedy resolution/propagation of name changes, deletions, etc. The monitoring software is pretty good.
If you're developing an extension, it's a four-step manual publishing process to update. No try..finally. The licensing model per certain kind of object encourages bad coding to try to save costs. The visual editor for interfaces goes crazy far too often, making the widget tree the only consistent way to edit them. The lack of built-in data migration is my biggest sticking point right now.
Value for money
Ease of use
Likelihood to recommend: 8/10