FiveM is an alternative online multiplayer for Grand Theft Auto V based on CitizenMP:IV. Required game version is 1.0.350.2 with all DLCs.
Unpack FiveM contents into "mp" folder created in GTA V root folder. The archive contains two files "CitizenFX.ini" and "FiveM.exe" Launch Fivem, wait for the multiplayer resources to be downloaded from the server. The launch is also done through FiveM. Signing up for a new Social Club account or we enter an existing one, we also go under the login in Fivem itself, then select a server and play. The connection should happen automatically, if it doesn't happen press "f9" to restart the server..
P.S. Multiplayer is now auto-updating. The official site will be listed under the author