Most users in the crypto-sphere are familiar with the idea of mining, where (hopefully) powerful CPUs and GPUs are set to "hashing" complex cryptographic problems to secure networks. This is called proof of work and prevents nefarious blockchain activities such as attempting to double-spend coins.
Most cryptocurrencies use either some form of mining to secure the network, called "PoW" (proof of work), or a voting mechanism called PoS (proof of stake), where holders secure the network by voting with a proportionate stake relative to their coin holdings. This latter method is how Steem operates.
However, as the cryptocurrency universe expands, new forms of mining and securing networks are being explored by new coins. Some of these can provide free profit on machines that are already running, because the power and load demands on "leased" hard-drive space are very small.
Burst is probably the easiest to setup and the most initially profitable. You install the Burst wallet, which is fairly easy to use, map out a plot on a drive with free space, dedicate that space to the network and start earning. Burst is even one of the few coins that is mineable on a 32-bit system; all you need is the Java client.
Cryptodave on YouTube provided some good profitability data for Burst, based on his 38.4 TB "leased" space.
April 2017 - 7230 Burst
May 2017 - 18974 Burst
June 2017 - 9030 Burst
At the higher price of burst in June/July, Cryptodave was seeing about $4.62 per TB per month, from 286 Burst coin per TB.
As of 8/13/17, burstcoincalculator.com estimates 130 Burst coin per TB per month. At current prices, that comes out to $0.72 per TB, per month.
As you can see, Burst favors those with large storage solutions, such as idle drives on servers that are already running. However, even at today's depressed prices, you can plug in a 5TB external drive and see $3.60 per month from space you were not otherwise using.
That may not sound like much, and indeed, it is not. However, Burst is a highly volatile coin and might be an excellent gamble. I would not recommend mining Burst to profit by immediately exchanging it, I would suggest holding it as a high-flying gamble. Mining a few Burst with empty drive space is an excellent way to do that for (nearly) free, while learning something to boot.
The word around the interwebs is that Burst crashed hard after "abuse was revealed." According to another user at Bitcointalk.org:
Another user reported later that a new team is taking / has taken over Burst. If Burst takes a substantial u-turn and the price correct back to July highs, the profitability on mining could move up 5x or more.
I would think of Burst like a lottery ticket. You're probably going to lose, and the main Burst website and forums have been down for days (at least, for me). Don't invest much, if you invest at all, but holding some could prove profitable. If Burst does make a comeback, this may be it's "blood in the streets" time to buy.
Note: The above does not constitute investment advice, and I am not an investment adviser. Do your own due diligence. My returns may not be worth mimicking, so choose to follow my entry points at your own risk. I do not advise trading, but holding coins you believe in off-exchange.
Sources: Cryptodave on YT, Bitcointalk.org, Burst.io, Coinmarketcap, Bittrex, Google, Youtube