What's a good ultra-lightweight e-mail client?

Preferably an IMAP4 webapp. I have an xampp server on my computer and an installer for roundcube mail, but my computer cries tears of molten blood whenever I try to run xampp’s mail server. I don’t like client-side applications because 99% of what I do with an e-mail client is reply to the two or three things in my inbox; they’re all far too full-featured for my needs. I have e-mail addresses from four places and don’t want to have to go to them all individually or use the crappy widgets provided by guggle or netvibes. So, anyone know or is hosting a good webapp?

And please, no Linux or Mac fundies.