I help administrate an instance of The City for my church, and it definitely is expensive and cumbersome. This FOSS solution looks like an awesome alternative, but is missing a few features of The City that would be hard to replace, like online giving, and childcare security (check-in, nametags, etc).

Yeah we don't have online giving.

Check-in is being beta tested at my church though, so be on the lookout for that in the next version :-)