I've been using http://workingon.co with hipchat to distribute the "what did I do today question" throughout the day. It works well for remote workers since they can easily forget an important detail after working in isolated conditions all day.
Also, read about the mobile first workplace design http://www.getdonedone.com/remote-first-approach-workplace/
Follow up: There are a ton of great apps in this space. Thanks for the comments and messages.
After weighing through everything - DoneDone looks pretty inline with our requirements - simple, email based for the customer ( no portal to log into ) and integrates with BaseCamp and Harvest which we use internally with no issues. Looks like they have a gorgeous v2 on the way any day now... http://www.getdonedone.com/new-donedone-coming-soon/
JiBit also very nice, no 3rd party integrations but very clean. Other notables are Groovehq, FreshDesk, BugHerd, HappyFox, and of course ZenDesk.
Anyone have success/horror stories with any of these?