The posts will be written for use in Swords & Wizardry Complete, so compatibility with other OSR rulesets should be spot on. They will be released under the OGL.
For example, here is the Elementalist Class I wrote for SWCL back in 2017:
The Elementalist Class for Swords & Wizardry Light
|Art by Brett Neufeld|
Elementalist Class for Swords & Wizardry Light
Elementalists get both spell like abilities and an elemental that can do their bidding.
Level HD Save BhB Adventures needed for Next Level
1 1 15 0 3
2 2 14 0 +4
3 2+1 13 0 +5
4 3 12 +1 +6
5 3+1 11 +1 +7
6 4 10 +2 +8
7 5 9 +2 xx
Elementalists have + 2 to Saves against fire and air bourn poisons. They can use daggers and staves, much like a magic-user.
They get the following abilities at each level:
Level 1: Summon Elemental (described below) Once per Day
Level 2: Gust of Wind - Can summon wind that can disperse papers, fan flames and knock over small (1/2 pound or less) objects Once per Day
Level 3: Breath Water as Air - Once per Day for 1 hr per level
Level 4: Dagger of Fire: Once per Day can summon a Magical Flaming Dagger. Only the Elementalist can wield it. It lasts for 1 round per level (throwing the dagger dispels it early). The Dagger is +1 to hit per level of the Elementalist and does 1d6+3 damage.
Level 5: Ball of Mud - Once per Day as the 2nd level Magic-User Web Spell, but this is made of mud.
Level 6: Fly - Once per Day as Magic-User Spell
Level 7: Fireball - Once per Day as Magic-User Spell
The greatest gift (and most dangerous, to the Elementalist as well as his adversaries) is the elemental they can summon.
The AC for a 1 HD elemental is 9 and improves by 1 point per HD to 3 at 7 HD.
Damage is 1d6, improving to 1d6+2 at level 4 and 2d6 at level 7.
The HD of the summoned elemental can be as many as the Elementalist has levels, but less HD then the max may be chosen. Only one elemental can be summoned each day and the death of an elemental causes damage to the Elementalist equal in HP to the HD of the elemental. Example: The destruction of a 4 HD Elemental causes 4 HP of damage to the Elementalist. Elementalists often dismiss injured elementals early to avoid this danger.
AC 9 to 3
HD 1 to 7
Damage 1d6 to 2d6