Bitcoin
- OpenBazaar - decentralized eBay.
- Blockai - proving ownership.
- BitPesa - cheap remittance, RIP Western Union.
- Blockstream - sidechains, allow new features on top of the Bitcoin blockchain without changing the protocol.
- Trezor - hardware wallet, secure your bitcoins.
Ethereum
- Akasha - decentralized social network.
- Slock.it - IoT and decentralization, e.g. rent your unused WiFi bandwidth, smart locks, etc. Previously: TheDAO.
- uPort - Identity and reputation services.
- Swarm - serverless hosting.
I sincerely hope to add a Decred section for the next update of this post.
Note: this is no investor advice, the topics and the solutions they propose looks very interesting to me, but I’ve no idea if there is a market for it and how they manage their companies. I was super excited about bonafide.io (identity and reputation services) which ended operations ~a year ago and TheDAO which resulted in an epic Ethereum fail (hard fork).