This very classical system-in-a-paddle is a pirate Atari VCS 2600 clone with 127 built-in games (but no cartridge slot). Produced in China, it was released under several brands (NICS in the US, SystemA in UK...) all over the world. This system was sold until recently in France by a local company : AKOR.
Everything you need to have fun playing good old 2600 games (excluding the TV set) is built in the system : CPU, games, control pad. While the second version (aka TV-Boy II) needs to be connected to the TV set via an A/V connection (SCART or standard RCA cable), the first one (TV-Boy I) includes a cheap wireless video transmission system : an antenna can be plugged into the RF Out connector, converting it in a (very) short range video emitter. You can also use a normal RF cable.
These two versions have a few other differences : the TV-Boy I has two Atari joysticks connectors which the TV-Boy II lacks (in two-player games, the pad controls both players at the same time...), and the version II has a better mother board design, probably in order to lower the production cost.
The system uses a bank switching technique and the 127 built-in games are accessed via an on-screen menu (the 128th program) so there is no dip switch as seen on some pirate x-in-one cartridges. This menu (that seems to be located at the lowest address of the ROM) is executed by default when the system starts and once a game is selected, there is no mean to come back, so one needs to restart the system to play another game.
Several games have been hacked : the copyright marks and original publisher logos were removed, and some sprites have been modified. Most of them have been renamed.
The SystemA and NICS versions of TV boy II, does not have the A/V connection mentioned. It's a straight RF lead to the TV. They also have a small II printed to the right and above the TV Boy logo. The game list is also slightly different.
A third version, the Super TV-Boy was released later, including the same games and specifications, but with a very different design.