The latest entrant is RetirementReady from Putnam Investments. According to an announcement, the nine portfolios have a target maturity date corresponding with the year the participant plans to start withdrawing assets. The dates are divided into five-year increments from 2010 to 2045.
The Putnam portfolios automatically reallocate and rebalance on an ongoing basis becoming more conservative as the participant gets closer to retirement. The ninth portfolio, the Putnam Retirement Ready Income Portfolio, is for investors on the cusp of retirement.