Free/open-source backup solution?

[nbarb99]

I've got Acronis TrueImage on my main machine for full drive imaging, and it works great. I'd like to also get a backup system going for the rest of the machines in the house, but can't afford dropping $(30 * 4) for a bunch of licenses at the moment. Are there any freeware apps or open-source projects that do drive imaging or backup? Anyone have any recommendations?

 

[nbarb99]

Update - for anyone interested, I found something that looks promising: DriveImage XML. It's pretty lightweight, and doesn't have features (AFAICT) like incremental and differential imaging, but it looks like it will work for my use.