Those that practice Miracles were mentioned in the previous post. This post provides a bit more detail. I also include a bit of rationale for the magic system as a whole.
In Microlite20, every spell as a DC target. This makes both Clerics and Magi skill-based spell casters. In earlier D&D there are no skill-based spell casters in the standard rules. Adding one to Andras or any retro-clone has a much different effect than doing it in Microlite20.
The same is true for any Mana based system. It doesn't exist in earlier D&D, but all spell casters in Microlite20 use their hit points as a mana pool. Varying how the mana is used doesn't do much in Microlite20. In fact, it looks like a record keeping nightmare. (Am I going to cast this as a 6th level Thaumaturge or save a point and cast it as a 4th level one?)
The classes themselves, however, offer an intended tradeoff. This is the element I want to keep. Over time, a Thaumaturge has to pay more to cast the same spell as a Wizard. At 15th level, a Thaumaturge will pay 9 points for a full Magic Missile while the Wizard will pay only 3. The gap closes as spell reach higher levels. At 21st Level, both the Thaumaturge and the Wizard pay 19 points for a 9th level spell. Yet, even at this high level, the cost for the Thaumaturge will continue to increase.
I also want to keep the feel of miracle magic. In other words, Shamans have strange and fearsome powers and Psions are regarded as atheists by the Priests. I like the idea that Psion create an issue of faith for a priest. This is further enhanced by the other changes that will make psionic ability much more similar to Priest spells.
Many telepathic abilities are similar to divination. A psion can determine a person's thoughts, discover the history of a place or item, travel astrally to be in a place far away in order to gather information and much more. Psions can heal. Psions can create things in a similar fashion as the gods (though not nearly as powerful as the gods). There's more, but you get the idea. Many abilities are already similar, so tweak the rest of the Priest spells to fit for psions.
Lastly, just like Priests can have various domains (or spheres in 2nd Edition), I have changed the Psionic disciplines from six to many. Just like 2e had Priests of Specific Mythoi, the framework is in place for GMs to create Psions of a Specific Path. This makes individual psions different based upon which school they attend. This is optional, just like the Specific Mythoi rules, but for a flavorful campaign, it feels a lot more fun.
Shamans are intended to be fun for the GM. I've almost ported over the D6 Fantasy Spell Building system to D&D. Since that spell building system has options for group casting, big effects, day-long rituals, etc, it becomes easier to build spells that just don't fit into the Vancian system.
For example, to create a spell that places a wall of force around an entire village isn't effectively possible. The spell caster would have to be a triple digit level spell caster to get a diameter that large. Using the spell builder, however, longing casting time and community help can make it possible. Not only that, it can provide a good measure of the appropriate level of this kind of spell.
Work continues on. Hopefully the next post will provide the new disciplines for psions and detailed examples of shaman spells.