I've seen plenty of Tulpamancers and Soulbonders on here, but I still don't really understand what they are and what the difference between them. I know they both have to do with systems, but that's all I'm really sure of.
Tulpamancers deliberately create their headmates. They start from scratch and create a person and build them up until they become their own person. Soulbonders have headmates just show up fully formed on their own.
There's quite a few differences between the two, and many other types of headmates besides just tulpas and soulbonds.
As Addy said, tulpas are intentionally created. They are developed over the course of months or years with the intention of them becoming separate and independent. The vast majority of tulpamancers I've encountered believe their tulpas are psychological in nature rather than spiritual - they're a fragment of the original that is nurtured and developed over time. Often they start off resembling children, and like all people they usually mature with age.
Soulbonds are spiritual in nature. They often show up randomly, but some systems can also invite them; from what I know, they are always fully formed when they arrive. I think one of the more common beliefs regarding them is that they are living their own life in another universe, and develop a connection with the host here through spiritual means. Via that connection they can interact with the host, and sometimes front. Most soulbonds seem to come from "fictional" sources, but not all.
But like I said, there's many types of headmate besides just these two! For example, fictives resemble soulbonds in that they originate from fictional media, but are generally seen as psychological rather than spiritual. Because of that, there tends to be a little more room for crossover between fictives and tulpas (whereas the potential for a mix between a soulbond and tulpa is practically nil). ^^
As an aside, its also rude to call one type of headmate another type. You don't call tulpas "soulbonds" or soulbonds "fictives". We actually hate the term fictive and don't want it used for my headmates, whether they are psychological or spiritual. I consider them spiritual because psychological stuff makes no sense to me, but other people might see them as fictives. As long as they never call them that, I don't care. The term itself is insulting to us.
The term fictive actually originated in soulbonding circles (I believe on LJ) for people who didn't like the mystical "woo woo" connotation of soulbond. Fictives and soulbonds can also overlap as they both seem to originate from a fictional source. But like @Charias said, theres no overlap between tulpas and soulbonds.
Ah, I wasn't meaning to imply anything there and I hope you don't take it that way! ;^^ Mainly I mentioned it because my headmate Aeolus is from a fictional source and identifies as a fictive, not a soulbond. Definitely seconding what you said as well - if anyone's ever unsure what particular label someone prefers, it's much better to ask them than risk getting it wrong!
I didn't take anything that way, no worries. I was just explaining that its rude to call one type another type. If you are unsure, you should ask, unless you see a person referring to their headmates a specific way, then it should be okay for you to refer to them that way. We just prefer the term soulbond, because its more spiritual in nature for us.