Recurring questions are what RichEdit's are available, where they are installed and what features they have. A relatively new question is which RichEdit's support the new Office math editing and display. So this post attempts to answer these questions. To answer the last question first, only RichEdit 6.0 has the Office math facility, although RichEdit 5.0 has a preliminary math capability that was good enough to get people intrigued with doing something well.
Before answering the other question, here's a quick summary of what RichEdit is in case you haven't heard of it: RichEdit 6.0 is a facility for getting plain/rich-text, single/multiline Unicode/ANSI edit controls and combo/list boxes in single world-wide binary that runs on all Windows operating systems. It has multilevel undo, message & com interfaces, considerable Word compatibility, richly formatted text, outline view, zoom, support for the latest IMEs, speech and handwriting input, rich complex script support (e.g., BiDi, Indic, and Thai), pagination, multilevel tables, autocorrect, hyphenation, kerning, ClearType support, autoURL detection, East Asian features such as vertical text, text wrap around embedded objects, font binding, and support for Unicode surrogate pairs and most Unicode 4.0 scripts. To some degree all RichEdit versions since 3.0 have had these features; although the support for them has improved greatly from version to version (Indic support was first available in 4.0). The rich-ink support was added in 5.0 (4.1 is used in the Ink Edit control that ships with the Tablet PC).
This post continues with a summary table, followed by a list of new features for each version. For the most part, each version has all the features of versions with lower version numbers. One exception is that the Japanese version of RichEdit 1.0 had vertical text display, which wasn't supported by later versions until RichEdit 4.0. Another is that RichEdit 1.0 was also pen-enabled and understood gestures for use with Pen Windows, while only the RichEdit 4.1 ink control and later versions have rich ink support.
If you want to use the Office 2007 RichEdit 6.0, you'll find it in the private subdirectory \Program Files\Common Files\Microsoft Shared\OFFICE12. Similarly the Encarta Math Calculator is stored in a private Encarta subdirectory. The OS versions are located in \Windows\system32. Maybe someday Windows will have the good fortune to have a more recent RichEdit than 4.1J But then we'd have to document all the new features L (Wouldn't be that hard…)