IThe 741 OP amp IC is very inexpensive yet is comparable to the best in respect of versatility and superb performance. We can't list every one of the 41 kits but here are a few examples: inverting and non-inverting AC and DC amplifiers,Voltage Follower, X'tal, magnetic mike Preamplifier, guitar,, telephone, Mixer, Intercom, AC & DC Motor Control, Multitone Bell, Electric Siren, Timer, Flasher, Voltmeter, Analog to Digital Converter....