Revision Diet is a plugin to limit the number of post revisions that are saved. I know that of the claims about how to turn off revisions and I have seen quite a few plugins that claim to remove revisions. Nothing I have done successfully prevented or limited the number of revisions being saved. Other plugins that I have tried hide extra revisions, but do not remove them from the database. One plugin I found looked like it would actually do the trick, but the author did not make any promises that it was safe to use. This plugin does not require any warnings. It does exactly what you expect – it allows you to set a number of revisions to keep for each post and deletes any revisions beyond that number. This number will not include the autosave revisions. If you set two as the limit that will allow two revisions plus the autosave revisionto be maintained. If you set zero, only the autosave will ever remain.
The options page is extremely simple – enter the number of revisions to keep and save your options. There is also a button to “Trim Excess Revisions.” This button will trim all the extra revisions from every post in your WordPress installation – this is useful (but never required) when you first install the plugin or if you chose to lower the number of revisions to save. As for regular use, each time you save a post the oldest revision(s) on that post will be deleted from the database down to the limit that is currently set (that will usually be zero or one revision deleted if you have previously run the “Trim Excess Revisions” function).
To install it simply unzip the file linked above and save it in your plugins directory under wp-content. In the plugin manager activate the plugin. Settings for the plugin may be altered under the Revision Diet page of the Options menu (version 2.3) or Settings menu (version 2.5 or later).