Besides IB's sim account, what are good free access simulators to test option strategies more or less realistically (I understand that fills can't be predicted precisely, but something which at least allows to enter simulated trades and show their progress somewhat close to reality)?
I find the easiest and fastest way is pen and paper using the bid/ask quotes from Yahoo Finance, or you could setup Yahoo Finance portfolio with a Yahoo email account.
If you are looking for software that models out positions and gives you the ability to simulate trades (although not 100% realistic) than Thinkorswim is the way to go. I think you can open an account and papertrade without having to put money in (or at least you used to be able to).