MLS 'Retention Funds' were implemented last season, but we hadn't really heard of them until this year, when it was revealed that Sporting Kansas City used them to re-sign Graham Zusi. Turns out that despite the fact that we weren't aware of them en masse as fans, teams were very aware of them, and they've been in use by several teams, including the Rapids.
Steve Davis from ProSoccerTalk put out a post today discussing the already widespread use of the funds, and included a list of the 14 players in question. Two of them are Rapids who were re-signed last season by the team, Drew Moor and Marvell Wynne.
He also included a pretty good explanation of what retention funds are meant to do:
The mechanism was designed to allow clubs to re-sign key players to new deals without pricing them into Designated Player territory. It was an effort to avoid damaging attrition, losing players we might classify as "above-average," or a few we would call "great" or perhaps "potentially great," to European clubs that might not look glamorous but could offer substantially greater compensation.
Teams supposedly have somewhere around $225,000 to use, and both Moor and Wynne have rather hearty contracts. That combined with the fact that most Colorado players are still young and won't be up for new contracts soon, and we probably won't be hearing about retention funds again for a while out here.