Ask HN: Suggestions on a WYSIWYG editor for email templates?

So we have been using tinymce as the basis of an email template builder directly used by our clients from our platform, but we are going to do an overhaul of our template/email design tool as it needs to get easier for clients. We of course can continue to use tinymce and work to resolve the problems we have had with it but it seems at least prudent to evaluate other options as we expect this to be a extensive update.

Any suggestions on WYSIWYG editors or other methods or what you have done (good or bad)? Our one hard limitation is we can't utilize a third party editor where the client would be off our site, it has to be integrated to our platform.

We are not against paying for the tool and I don't want to reinvent the wheel here, but I'd prefer open source. We need compatibility across current browsers but we have no requirement to support IE8 or lower. We have even considered writing a custom tool here, but it seems prudent to instead add components to existing tools if possible (time and money wise).

ideas?