Online multi-system emulator websites are handy, as they enable you to play and enjoy retro games from multiple systems - without needing to install emulator software, BIOSs, ROMs etc first. Nor do they require the complicated installation and setting up procedures that some emulator programmes require.
Most online multi-system emulator websites enable you to configure the controls and take 'snapshot saves' of your progress - regardless of whether or not the original game had configurable controls or a save game feature.
My Emulator Online is an example.
I'll post links to others as and when I find them. Suggestions welcome.
Obligatory legal disclaimer bit: Nomad's Reviews is unable to officially endorse the use of any specific system, emulator, website etc and accepts no responsibility for the user's experience.