- Movable Type Open Source (MTOS) -- The core engine without any extensions/packs, minimal base for blogs et sites (more or less equivalent to MT 4.1 without Custom Fields). Free for all uses.
- Movable Type (MTOS?) -- Developer edition, same as MT open source above. Free for development purposes.
- Movable Type Pro (MT) -- The main and most interesting edition, contains MT plus the Professional Pack (Custom Fields, Universal Templates) and the Community Pack (formerly known as MTCE, Community Edition). A really powerful pack allowing one to create blogs, sites and communities. Exists in two flavors/licences: the free Blogger edition for "power bloggers" (i.e. individuals even if the usage is commercial, with a $99 support option), and the Business edition (for commercial entities) with support and more affordable licences than the previous MTCE (at the strange "psychological" prices of $395.95 for 5 authors and $1,499.95 for 20 authors, including support).
- Movable Type Enterprise (MTE) -- For those companies who want to pay a big premium for the privilege to hook up the same product as above to their LDAP directory and proprietary databases.
My two cents in terms of marketing:
- I don't get the MT Open Source / Developer difference. As a developer, I would use both MTOS and MT Pro for different development purposes.
- I wish Six Apart would stop renaming/reshuffling those names and packs at every release! (P.S. But heck, to be fair, I love the MT Pro combo, MTCE was overpriced and not promised to a brilliant future as a standalone product)