Small Caps
Small caps have a long typographical history. For the past several hundred years, they have been used in the print medium to create a aesthetic distinction (e.g. by linguists) or as a substitute for a long string of capital letters which may appear jarring to the the reader (e.g. for long acronyms). Check out the small caps Wikipedia page for more info.
As you might have noticed, the small caps Unicode alphabet is probably the most "complete" of the three glyph sets that the engine behind this website uses. The Q, X and S letters aren't quite right, but they're passable.
If you're trying to produce small caps with CSS (within your HTML document), you can use this code:
<span style="font-variant: small-caps;">Testing 123</span><span style="font-variant: small-caps;">Testing 123</span>
You could instead use the small text characters generated by this website, but you'd be better off using CSS because the rendering will be better. But often you don't have access to HTML tags, and so that's where a generator like this might come in handy.
Like I said earlier, people often think that the text produced by this generator is a small caps font, when actually it converts your text into a set of small caps characters or "glyphs". However, if you're actually looking for a font that supports small caps, then you'll be happy to know that most fonts do support small caps in at least an "inferred" manner. That is to say, if the small caps unicode characters aren't explicitely in the font, then the renderer (the browser, word processor, etc.) should be able to automatically scale the regular Latin characters to create symbols that look like small caps. Of course, these won't look quite as good as if the small capitals were actually created by the type designer.
Here's the full small caps alphabet used by this generator:
ᴀʙᴄᴅᴇꜰɢʜɪᴊᴋʟᴍɴᴏᴘǫʀsᴛᴜᴠᴡxʏᴢ