It's not exactly a manifesto...it's not a constitution...people aren't completely sure what it is. The Contract from America, envisioned by young conservative Ryan Hecker and organized and promoted heavily by FreedomWorks, the Tea Party Patriots, and various other conservative groups, will provide a statement of principles to be loosely adhered to by the Tea Party movement that will be unveiled April 15, when the tea partiers come back out for another round of nationwide Tax Day protests.
It's a crowd-sourced document--people can go online and vote for their favorite principles. The list of principles is being whittled down from the 21 listed below.
Don't expect this document to necessarily be adopted by the tea party movement as a whole: the groups promoting this document represent a broad and influential faction within the tea party movement--but it is a faction. FreedomWorks, Tea Party Patriots, and their allied groups don't typically get along with other groups like Tea Party Nation and Tea Party express. Other groups like SmartGirl Politics straddle the lines of affiliation.
For what it's worth, Newt Gingrich, who engineered the original Contract with America, likes the idea of the Contract from America and said as much on-stage at the Conservative Political Action Conference in DC, where some tea partiers were in attendance.