The Keepers Registry currently has 8 participating archiving agencies:
- British Library (10 September 2013)
- CLOCKSS Archive (10 September 2013)
- Global LOCKSS Network (10 September 2013)
- HathiTrust (10 September 2013)
- Portico (10 September 2013)
- Archaeology Data Service (2 August 2013)
- National Science Library, Chinese Academy of Sciences (5 July 2013)
- e-Depot (24 April 2012)
A quick look at their descriptions suggests that some may be interested in archiving MathOverflow.
The Center for Research Libraries appears to be the main international entity for assessing and certifying the trustworthiness and reliability of major archiving agencies. Some reports can be found here.