I am developing my own Lovecraftian magic system for use in Traveller and the Cepheus Engine. This will be especially useful with my Hard Space near-future, near-Earth Lovecraftian setting.
In a nutshell, under this system, anybody can attempt to learn spells by studying Mythos tomes; anybody can attempt to cast any spell. And there are no spell points or "hard" daily "spell slots".
- Learning spells has a Sanity cost. So does studying the tomes to begin with. Learning also requires an INT throw to successfully learn; failure means you need to repeat studying it, again - with a Sanity cost. The more powerful the spell, the harder the INT throw to learn it.
- Spells take time to cast; in many cases, hours. "Combat" spells, which are often weaker, usually take two full combat rounds to cast, and concentration might be broken if the sorcerer received damage while casting the spell.
- Spellcasting requires an Occult skill throw. Fail or roll "snake eyes" (there is no automatic success in spellcasting), you'll get the spell's integral "miscast" result. The stronger the spell - the nastier the miscast.
- The really powerful spells damage your Sanity on failure and/or on success (Commune with Cthulhu at your own peril!). So you can technically attempt to cast any number of spells a day as you'd like, and a totally clueless layman can try to learn and cast magic (with the usual DM-3 Unskilled Penalty), but the limiting factor is the risk you're taking (a very, very powerful limiting factor), as well as casting time. Cast as many times as you dare and as the casting time allows you - at your own peril!
Yes, this means that even skilled sorcerers will sometimes fail in spellcasting - at least once in every 36 spells (on average - the chance of "snake eyes"). This is H.P. Lovecraft's legacy we're talking about here - not Dungeons & Dragons. Sorcerers do not cast powerful magic casually. They may use weak spells more often, as the risks of failure for them might be bearable, but no no one takes powerful summoning and necromantic magic lightly.
This, of course, leads to all sorts of sorcerous disasters (read: adventures), as - for example - some utterly unskilled fool is just bound to try casting that 6th Circle earth-shattering summoning spell, unleashing something horrid upon the local colony!
The above were just initial thoughts and ramblings. I'll write up a more coherent magic system later on.