Since the new version of Release Management was introduced in TFS 2015.2 it has been in trial mode, anyone with at least a TFS CAL/Basic License could use it.
Based on the old Release management system I thought that you would need Visual Studio Enterprise to create releases when the trial was over, I was wrong. From TFS “15” RC2 1 all Release Management features, including authoring of release definitions, are included in TFS CAL. Stakeholder can as before approve or reject releases.
From now you can run one release pipeline at a time for free, additional releases that you create will be queued automatically, additional pipelines will cost $15/concurrency each month or it looks like you will be able to utilize Visual Studio subscriptions in increasing the number concurrent release pipelines .