One thing I found which I think is similar but much more flexible is TiddlyWiki. It is a self-contained wiki (uses javascript and inline CSS to keep it in one html file) that is focused on the Getting Things Done model of productivity. I used it for awhile but got frustrated with how to take it along with me to other computers or host it securely on my server. Once you get your brain around it, I think it works as well or better than Backpack.

Since I am a Google groupie, this approach to putting todos in your Google Calendar sounded real nice, though I have not tried it yet.

The focus is on cleaning up our:
a) House – We hired a maid to come every 2 weeks for $50 a trip. An investment.
b) Table – The kitchen table is not a holding area, it is a place for our family to have dinner together. Clearing it off and scheduling meals together on Google calendar isn’t trivial.
c) Transportation – We bought a mid-sized import SUV that gets 22 MPG instead of a full-sized domestic SUV like all our friends in Dallas. No harming the environment for us.
d) Our Mouths – We are done with the catty bickering that sometimes gets mumbled during exchanges in the middle of the night as we tend to crying children.
e) Finances – Auto bill pay, more consulting on the side, and an agreement to track our spending.
f) Calendar – Using Google Calendar to track every member of the family so as to not double-book and to schedule blocks of quality time that otherwise has to happen by circumstance.

So, yep, we have a little administration stuff going on as well. Cleaning it up!