The Ohio State summer class schedule is viewable at the end of each January. (Before the summer schedule is released, you can make your best guess at will be offered next summer by looking at the prior summer's class schedule.)
If you are a student who would like to schedule summer classes at another institution, we encourage you to check in with an academic advisor.
One tool you can make use of to see how the classes you take at another institution will transfer back to Ohio State is Transferology.com. (Note: if the class you want to take and/or the college you want to take it at is not listed, it does not necessarily mean that the class will not transfer back to Ohio State as the equivalent you are hoping for, but it does mean you will need to submit a syllabus for the class to the appropriate Ohio State department in order to get a pre-evaluation.)
Please note that Ohio State's Math Department will not allow students taking a math course at another institution to enroll in their next math class at Ohio State until the final transcript is sent to Ohio State. See math's departmental website for more details on transferring math credit.