Yeah definitely, we used Pivotal Tracker for a long time ourselves. There's a lot to be gained, particularly from a scheduling and reporting perspective, by having estimates but without the strict sprints of Pivotal.
not exactly estimating, but I built something to let the team vote on items in a Trello list. We usually vote more along the lines of "bang for the buck" ie importance/estimation http://blog.forcerank.it/tame-your-trello-backlog