By the site’s definition, practical languages include things like C, Java, Python, and Perl. There’s also old school stuff like FOCAL-69, Fortran, Algol, and APL. There’s several flavors of assembly and plenty of other choices. On the recreational side, you can find Numberwang, LOLCODE, and quite a few we’ve never heard of.
The site is interesting if you are wanting to compare languages or try out a snippet of code you found online. For practical use, it probably isn’t going to help you much. Some languages lend themselves better than others to the site’s simplistic interface.
When you select a language you’ll go to a page that looks the same no matter which one you chose. You can enter compiler flags and–of course–your code. You can also enter a header and a footer. It isn’t really clear what the advantage of that is over just having one big blob of code. There’s no way to put in additional files like headers, other source files, or anything. Just those three text boxes.
There are separate boxes to provide standard input and command line options to your program. When you press the play button at the top of the page, the output appears in another text area and an area labeled debug give you statistics about the compile, not a way to debug your program. You do get error messages there, though, if there are any.
The site is free from ads and other nonsense other than a call for donations and a plug for their web host on the main page. If you wanted to set something up like this on your own server–perhaps for classroom use–it is open source, so you could. We’d love to see a bunch of old retrocomputer languages set up like this.
If you want a hardware version of one of the more offensively-named recreational languages, there’s an Arduino shield for that. If you use the site to write some killer FOCAL-69 code, perhaps we can interest you in a Raspberry Pi based PDP 8.