I'll say this: it is <strong class='bbc'>not</strong> a <em class='bbc'>Cave Story</em> mod, it's definitely not a <em class='bbc'>Spelunky</em> mod, and it's not a <em class='bbc'>Little Fighter 2</em> mod. However, it will have the two protagonists of <em class='bbc'>Shane's Cave Story</em>, both the current version and all the planned sequels (of which there are four planned sequels).
And here's some posts related to Project Secret. <a href='http://shane.freeforums.org/post4742.html#p4742' class='bbc_url' title='External link' rel='nofollow external'>Link to random chatting thread with posts about Project Secret. Although most of it is a secret.</a>