Roundcube, and SquirrelMail are the two alternatives I can think of. Last time I tried Roundcube was years ago, so I don't know what the state of it is now, but it was an attempt at a more Gmail-ish interface.
1. I don't think that Node.js specifically is the answer.
2. Most of the alternatives are just web-based front-ends to IMAP. My feeling is that to make a 'true' OSS Gmail alternative would require an integrated solution (i.e. an 'email system' with SMTP, IMAP, Web interfaces).
3. I think that the 'state of the art' has languished because everyone has doubled-down on Gmail, and the (now defunct) free-tier of Google Apps for Domains.
You could easily just use another email provider that will take care of the "sewer of pain" while you use a web-based IMAP front-end (or develop your own).
