If you're a long-time PC user, and remember accessing BBSs, or playing DOS text games like NetHack or Rogue, then you'll be familiar with the "IBM Extended PC Graphics Character Set", now known in Windows lingo as the "OEM Character Set". If you're not, then here's a quick explanation.
When the PC was invented, the character set used by almost all PCs was known as the ASCII Character Set. But the ASCII character set only specified 128 characters, and the IBM PC (and most other micro computers) could generate 256 characters. What to do with those other positions? The answer in most cases was to use the extra space for foreign characters, strange symbols and lines for drawing tables. People used these extra characters to design better looking menus, cool logos and all sorts of stuff. And of course, you could save those creations off to disk to be viewed later.
Thing is, Microsoft Windows uses a different default character set, called the ANSI Character Set. It defines all 256 characters (although there can be some variation to the second 128 depending on your country), and while the first 127 are identical to the ASCII character set, the rest of the characters are quite different. The result? If you view a text file that was created using the OEM Character Set using a program like Notepad, it looks wrong! The wrong characters are used!
OEMViewer uses the OEM Character Set, so those old files look as they should. It can view text files up to a reasonable size, you can change the size of the font and of the window, and it even handles files that only have a <CR> or <LF> character at the end of the line, rather than the PC "standard" or <CR><LF>. It's also really quite tiny!