When Baekdu opened, I made a Raja there, but was focusing on Siege Perilous so never logged back on there until Mugen came out about a month later. I made a Raja on Mugen and divided my time between Baekdu and Mugen, and some Siege Perilous. If I remember correctly, Baekdu only had a Felucca and Mugen had both Felucca and Trammel. Freja is correct, all three shards operated on the Siege Ruleset, even Mugen Trammel facet.
Baekdu was like a dead shard almost right away, at least compared to Siege Perilous and Mugen when first opened. I do miss Baekdu, the little people that did end up playing till the end on Baekdu eventually moved back to a production Korean shard, or onto Mugen.
Mugen is much like Siege Perilous, but with extra land. Most folks do their own thing and won't be seen in towns much, just like Siege Perilous. Most players there do not use GC, not sure why. Lots of roleplayers on Mugen. The town/bank of choice is at New Haven. Player prices there are much cheaper compared to Siege Perilous. I am assuming most production players placed a second house on Siege Perilous, and of course, brought the production economy to Siege Perilous.
On a side note, I am always interested in Mugen trades. I can pay/trade with Siege Perilous, Atlantic, Napa Valley, Formosa, or Europa gold/items.