Which one is the closet out there? I want extra bold, extra light, bold, regular and medium. Thanks :)
Have a look at google fonts.
There you can find high quality fonts that you can use anywhere for free.
Be aware that no free font would be almost same to 'Helvetica' but you can get similar feel that you would get by using Helvetica.
Have a look at Google Fonts' "Poppins". The are various weights available. It's not identical but close. The main differences are the single storey lower case "a", rounded tittles, and straight descender on the lower case "y".
Here's a quick comparison, you can check the others yourself.
Another one is Arimo