the safest and most stable sites to invest !
join aslong as the hashrate is cheap ! halving comes soon!
http://bit.do/moneyocean - they will give you free 15khz/h mining power to generate btc
http://bit.do/rapidmine -another 15khz for you without paying anything !

http://bit.do/minetop - will start you up with 5tx miningpower (their own system as they got their own algorythm)

http://bit.do/Coreminer -50GHZ miningpower for signing up and supercheap to get additional power! + open a chest on purchasing and get even more!

http://bit.do/mineflare -nothing free here , but cheap buy in and constant investment of your earnings as they will not go down (just purchased the new generation of miners) and have been around quite some time