The "XL741" Discrete Operational Amplifier kit from Evil Mad Scientist Laboratories is a faithful and functional transistor-scale replica of the μA741 op-amp integrated circuit, the classic and ubiquitous analog workhorse.
An Operational Amplifier, or "op-amp" as they are commonly known, is one of the most useful and common types of analog electronic circuit building blocks and the XL741 kit was designed by Eric Schlaepfer, in collaboration with Evil Mad Scientist Laboratories is lovingly designed to resemble one.
The XL741 kit is sold as an easy-to-build soldering kit. It includes the circuit board, resistors, transistors and capacitor that make up the electrical circuit as well as printed assembly instructions. The kit also comes complete with the "IC Leg" stand, and 8 color coded thumbscrew terminal posts.
Basic electronic soldering skills are required, but no additional knowledge of electronics is presumed or required and it should take about an hour to build.
The XL741 circuit is a direct implementation of the "equivalent circuit" from the original Fairchild μA741 datasheet. It comes with terminal posts and solder points so that you can actually connect to it and build up classic and functional op-amp circuits.