Honeygain is a platform where you can sell access to your internet IP for the company. You get paid $0.10 per GB of data used, and the amount of data used by them depends basically on the company's activities and interests.
According to their website, internet access is used to make SEO and Web stats, verify ads, test apps, deliver content, compare prices and protect brands (for example, via finding illicit copies of materials).
Honeygain offers a $5 bonus for new users from their referral program (click here to create your account!). Moreover, they pay you 10% of the earnings of each user you referred, which can increase your revenues. They also offer a 'honey jar pot' with extra prizes for daily login (they vary from $0.01 to $0.10).
They stipulate a minimum of $20 withdrawal, and you get paid via Paypal or in BTC.
It's necessary to download a program (for desktop) or an app (they're Android-friendly, not sure about iOS) and to link your account to it. The program doesn't use much power if we're comparing its consumption to the one of a computer. But smartphones and tablets can have a smaller battery duration if the program is running in the background.
My earnings
I have started to use Honeygain in June and now I have $11.55 in my account. It runs mainly in my notebook (I think mine stays on for about 8h per day, on average) and occasionally on my tablet. So what I got was $6.55 in 4.5 months, that is, $1.46 per month. I really forgot about it during big periods of time, and I also had holidays in July-August, when I almost didn't use my computer, so it seems not bad in general! I mean, for an investment paying 1% per month (12.68% APR), I'd need $146 to do so, thus it's like if I had a 'free' investment of this amount at this rate. It's true that I don't pay for electricity (it's included in my rent), but it's also true that if you only run your computer when you would already do so, the difference in power consumption is negligible.
It's possible to connect up to 10 distinct devices, which can strongly boost your earnings!
I've earned $5 from the initial offer, $4.92 with my computer, $0.54 with my tablet, and $1.11 with the daily login earnings. Here, you can see my earnings from the last month:

(1000 points are worth $1)