Recommend generally avoiding the term partly for the reasons stated by rms and partly because some OER simply don't seem like "content" to me (e.g. interactive simulations, Moodle, ...).
In general, an appropriate and more specific term can be used in context (e.g. simulation, LMS, tool, practice, ...), but otherwise, the following could be used:
- ... ?
When "content" is part of a well established term, phrase or acronym (e.g. CMS), it might not be too productive to use/invent an alternative.