I've been working on a site that required the restriction of post titles from within the CMS. It would have been easy to wrap the title in a
substr() but that would have left the client confused as to why half of their title was missing.
I couldn't find anything that would do this so I put together a little plugin to restrict the title via JS. Not infallible and easily circumvented but the purpose was just to solve an issue of usability for the client.
Limit Post Titles Plugin
It's a pretty simple plugin with a single settings page to control which post types to limit and to define the character limit.
It'll then add a little counter to the title field on the selected post types.
If the character count of the field exceeds the limit the counter will go red and the publish button completely disabled.
The plugin can be downloaded from the WordPress repository or directly from GitHub.