I gave this forum its title because I think those three things represent a good way to look at things. Individual systems will likely have both one (or more) of the three on which they focus, and then their own approach within that, so the big picture can go from clear to cloudy in the blink of an eye once you start listing every approach.
I will comment on the things I'm aware of and that have a current connection to StrongFirst - I'll tackle your list at the same time. Before I do, allow me to recommend a page on my web site that addresses all of Pavel's flexibility and joint health materials plus a few more. All these are or were at one time published by Pavel's old publisher.
Flexibility Guide from kbnj.com
Pavel's
Beyond Stretching is an older book about joint health and flexibility, superseded by the three books immediately below:
Pavel's
Super Joints is about joint health.
Pavel's
Relax Into Stretch and
Forced Relaxation are about flexibility.
For everything below, I am necessarily simplifying - please don't take me to task by saying, "You know, this program addresses more than you just said it does." All of these are successful programs that have undoubtedly been of help to many people, but I'm writing a forum post and not a book-length review here.
FMS stands for Functional Movement Screen and belongs in our Movement category. It has a strong connection to StrongFirst - joint programs have been and continue to be offered, and several high-ranking StrongFirst leaders are also leaders, teachers, and authors of material related to the FMS.
Flexible Steel is the name of both a book and a program founded by Master SFG and Tae Kwon Do Grand Master Jon Engum. The book acknowledges Super Joints and Relax Into Stretch as foundational materials for its program. It addresses both joint health and flexibility. Many people, including me, serve as leaders in both programs, e.g., as of this writing, I am looking forward to co-teaching a Flexible Steel Level I instructor workshop a week from now with another StrongFirst Senior SFG,
@Pavel Macek.
Ground Force Method was founded by Master SFG Peter Lakatos and its United States coordinator is Senior SFG Andrea U-Shi Chang. It's focus is movement. I took part in a one-day training in this in 2012 but haven't done anything with it beyond that.
Kelly Starrett's work is well thought-of by FMS co-founder Grey Cook - I have seen video of the two of them together discussing each other's approach to helping people move better. I don't know anything else of Kelly Starrett's work other than that, but an endorsement by Grey means a lot to me.
Original Strength is a program founded by two people who used to be associated with StrongFirst. Original Strength has since announced partnerships with at least one of StrongFirst's direct competitors, and has also announced programs that address things already addressed by some of our current partners. I feel strongly about what we do here, and equally strongly about the relationships that our organization has chosen to foster and those with whom we have parted company.
Systema is, to the best of my knowledge, a Russian martial art. I confess to knowing precious little about it.
MovNat is another thing about which I know very little.
There are other organizations we could mention here, e.g.,
Z-Health, which some current and former StrongFirst people participate in, and which I have found to offer a useful approach to flexibility/joint health/movement.
@TravisDirks, it's not possible for this list to be exhaustive, but I've taken your list and commented on everything in it, plus another thing or two, and I hope my admittedly personal perspective is helpful to you and to anyone else reading along.
-S-