GenPlusDroid has easier access to rewind than Retroarch and is also free.
There is an unofficial updated version of Mupen64Plus AE with many internal improvements over the normal build.
You may have to sign up to get it from an attachment in some random topic or from inside the shoutbox.
You'll need Retroarch for the Sonic hacks (like the recent contest ones) since some only work properly on the Picodrive core.
Thomas was everywhere...