There is no free local tour, nor free tourist visa in Addis Ababa at this time.

ET will SELL you a city tour during your layover, but that is very poor value judging by the prices I've seen. And if you need a tourist visa, you need to apply for an eVisa at https://www.evisa.gov.et before your departure.

On eligible itineraries, you will receive the standard STPC voucher at check-in which includes transit visa, hotel, transfers and meals. You take the voucher and go directly to immigration upon arrival in Addis. Then get the voucher stamped at Ethiopian Airlines transport desk immediately after exiting customs - they will direct you to the appropriate hotel shuttle.

For a comprehensive discussion on Addis stopovers check out this thread : Ethiopian Airlines (ADD layover)