I'm running two of the same ones from that list 3 years ago ( http://www.twiddla.com/ and https://www.s3stat.com/ ), and have just launched another one ( https://unwaffle.com/ ). Every year that passes makes it easier to get something like this off the ground, as the infrastructure becomes cheaper and more ubiquitous, and the knowledge you need for the business side get better packaged into step-by-step guides. It's…
How are you promoting your products? I am part marketer and part developer, but I am finding it difficult to market to developers :) I recently launched http://www.smsinbox.net for Twilio devs, and am slowly gaining some users, but finding it very difficult to reach the target audience, and/or get visitor/user feedback.
Take a look at s3stat.com above for a good example, it's much more polished without much more content.
[1] I send a few thousand SMS a month via Twilio for thesimplepostcard.com