- Open source projects, like RepRap. These operations aren’t necessarily companies, let alone something you could invest in, other than donations.
- Small companies, like MakerBot. They’re privately owned and unless you know someone you’d have a hard time making a real investment. But investments do happen, as MakerBot recently received a massive USD$10M injection.
- Private companies, like Objet or ZCorp. They’re big. They have (presumably) big profits. But you can’t invest in them, as they are private. No stock offerings here.
- Public companies, such as 3D Systems or Stratsys. Yes, you can invest in them! They are public companies offering stock that trades on major exchanges. But here’s the catch: only these two 3D printer manufacturers offer stock. You may choose one or the other. Only.