It’s a hobby: Taking on-board diagnostics information from the in-vehicle networks and observe and analyze them on a PC. Of course you want to pay as little as possible for the interface. That is why cheap, faked products are offered more and more often.
The ELM327 is a pre-programmed micro-controllerboard produced by ELM Electronics (Canada). It translates and interprets the on-board diagnostics (OBD) data. All of the mandated OBDII (on-board diagnostics) protocols, amongst them CAN and J1939 are supported. The CAN interface operates in the silent mode. The ELM327 command protocol is a popular OBD-to-PC interface and is also implemented by other vendors. When looking for ELM327 diagnosis interfaces, one can find a lot of relatively cheap products on Ebay and similar webpages. Original products are built, amongst others, by WG-Soft, a German company. According to the company’s website, many of the cheap products found online do not in fact include the ELM327 interpreter chip, which is a protected brand name. For reading out the OBD data, the chip is accessed by software, which WG-Soft also offers.
To see what to look out for have a look at https://can-newsletter.org/tools/tools-miscellaneous/nr_elm327_wgsoft_140123/