This is Mike. Edgar (called ?Lucid? here on the forums) and I are the co-creators of Spriter.
Spine is indeed a lot like Spriter, in fact it was at least inspired in part by Spriter. To paraphrase from their comments, they were excited about Spriter and had been part of Spriter's forums but felt Spriter was taking longer than they wanted to wait and they worried Spriter would lack some of the features they wanted in a modular editor for the purpose of making their game project, so they decided to make Spine.
Here's some things you should know about Spriter when comparing the two tools:
1) Spriter is indeed taking longer than Spine to get to a version 1.0, but this is in very large part due to the intended scope and feature set we have planned for Spriter as well as our commitment to cooperation with the game development community during its development. An example of theses points is Spriter's data format which we took the extra time to make open from the beginning and co-developed with the community to insure the most flexibility it could offer while also insuring it would be very easy to add new features later without breaking backward compatibility.
While our next build (which is getting close to being released) has a feature-set similar to that of Spine, we consider it and even the first version of 1.0 to be very much just the beginning of Spriter's development. Spriter is not just a tertiary product we're releasing on the way to making games, we are very dedicated to its continued growth, increased flexibility and useability. We both love designing and making tools which empower creativity and reduce the need for tedious aspects of game creation, and Spriter is the focal-point of that passion.
2) Even though Spriter isn't at 1.0 yet, we have always provided and will continue to provide a well-featured free version of Spriter with the ability to export the actual optimized Spriter data for use in games. You can download the current beta version from here :
Many people and game studios are publishing games with animations create with Spriter, and many more are doing so by the day.
3) I think this point is the most important. Full Spriter support for Construct is already in the works and is a very high priority for us. See here:
Spriter Plug for Construct 2
Both Edgar (Lucid) and myself (Brashmonkey) are long time Construct users and supporters. (Check out how many plug-ins, feature improvements and bug-fixes Lucid has contributed to Construct Classic). I'm not mentioning this to pander for community support, but pointing out that Edgar and I have always had full, easy, and extremely flexible Spriter support for Construct 2 (and classic) very much in mind from the very inception of Spriter. In fact, the original Kickstarter campaign release of Spriter was made using Construct Classic. Because we are making our games with Construct 2 ourselves, its most definitely in our own best interest to get and keep Spriter and all of its up-coming features fully supported in Construct.
As you can see, we've already begun working (with Ashley I should add) to not just add full Spriter support for Construct 2, but to do so in as flexible and optimized a way as possible...not just a quick logic-port of generic Spriter API to get it working...We want it working as best as possible, specifically for Construct...and as nicely integrated into Constructs plug-in UI as possible.
Thanks for the kind words about Spriter's intuitiveness. It actually will be further improved in that regard after all the 1.0 features are in, once Edgar has the chance to put in all the mouse-over descriptions and first time user pop-up dialogues etc. Also, While currently Spine has a few features we do not, the next and future build releases will quickly rectify that.