My $0.02:
The big chip is a Philips P87C51FB-4N. Logic Function Number:87C51; Memory Size:256 B; Memory Type:RAM; Microprocessor/Controller Features:16000 bytes OTP PROM; No. of Bits:8
This is a 8051-type micro controller (like an ATmega168). OTP means one time programmable (like a CD-R), so you can't reprogram it like a modern micro with flash. Even if you could, you would need to have tools like a programmer. Probably useless, except for something like solder practice.
ADC0848CCN - 8-Bit uP Compatible A/D Converters with Multiplexer Options - National Semiconductor
Low end 8-channel analog to digital converter. Looks like a parallel bus, not great for interfacing with modern MCU's that lack an external memory interface, but usable. You could use it if you need more analog inputs than your MCU has available, but have plenty of spare digital pins. Buying a MCU with enough inputs is usually the cheaper solution, though.
LM324AN Low Power Quad Operational Amplifier
Popular quad jellybean op-amp, quite versatile, but pretty cheap.
4N25-X009 Optocouplers
Optocouplers are used when you need galvanic separation, for example in switching power supplies, where the secondary side should be floating relative to the mains, but you want to switch the MOSFET on the mains side.