Smartsteem.com is a website where you can buy upvotes, sell upvotes or delegate Steem Power. The last 2 are amazing ways to earn passive income if you can't be on Steemit for a period of time.
What I like about the Smartsteem website the most is that they have a really nice revenue calculator.
You just introduce your Steemit username or the amount of Steem Power you have and you will get some estimates of how much SBD you will earn daily, weekly and monthly.
As you can see, if I would be inactive on Steemit for the next month I could just sell my upvotes through Smartsteem and earn about 1SBD/month completely passive. I will also get curations reward which are not included in the revenue calculator. This might not seem much but keep in mind that I only have 40 SP. If you have more than that the income will obviously be bigger.
They also have a referral program in which you receive 0.5% of every vote sold by the friends you referred (subtracted from smartsteem profits ).
If you think you might be interested in this and don't have an account yet, you can sign up using the link bellow. You don't need to create an account, you will sign up using steemconnect. ( Ref Link )
SMARTSTEEM