Especially good for Tibetan...

[Stream-of-consciousness style; apologies:]

No BiDi or RtoL support, but it seems to support much of Arial Unicode (at
least). (I didn't try CJK, yet.) Not bloatware; download is under 900kB.
Plainly, a *lot* of work has gone into this. Seems to be undeservedly
obscure. With Arial Unicode installed, it does appear to compose Tamil,
but I don't know about reshaping and glyph combining. I've been exploring
it for about half an hour, and feel that it might be worth a look.
Apparently, it can embed images into the document it creates, which might
be of considerably use to linguists, because it apparently can include
images. Creates HTML e-mail, which won't please everyone; also utf-8 and
utf-16s.

Runs on any Win from 98 SE to XP, inclusive.

For people who don't need Tibetan support (which appears to be really
extensive!), there's an option to disable it. Restart it, and there you
are.

Unicode ranges are handled by a character picker that uses installed
Unicode fonts (of course). Mouseover selects a character, which appears
magnified in a small window; a left-click types it. Support for other
keyboards doesn't look great, but I'm far from sure.

<http://home.alamedanet.net/~tibet/udp/>

Have fun,

--
Nicholas Bodley /*|*\ Waltham, Mass.
Opera 7.5 (Build 3778), using M2