What happened

Shares of 3D printer-maker Stratasys (SSYS -0.20%), which have tread water for most of the past week, took a sudden turn to the upside on Friday, roaring ahead 10.2% through 12:40 p.m. ET. Rival 3D printing concerns are racing higher as well, with 3D Systems (DDD -0.86%) rising 10.4%, and Desktop Metal (DM -2.34%) up a solid 5%.

Why all the excitement about additive manufacturing technologies today? Because this morning, we learned the rival 3D printer-maker 3D Systems is interested in buying Stratasys.

So what

Seriously, folks, this Stratasys saga just keeps getting more and more curious.

Barely two months ago, the story began when Stratasys competitor Nano Dimension (NNDM 2.03%) -- which already owns a 14% chunk of Stratasys -- expressed interest in buying another 38% of the company, so that it would own more than a 50% stake in Stratasys, and thus have effective control over its rival.

Stratasys was understandably less than enthused with this prospect -- despite Nano Dimension offering $18 per share for its shares, a significant premium over Stratasys's stock price at the time. So last week, Stratasys announced that it was planning to buy yet another 3D printer maker, Desktop Metal (DM -2.34%), presumably with the aim of scaring off Nano Dimension and keeping Stratasys independent. (Interestingly, Stratasys valued its own shares at only $15.26 in making its bid for Desktop Metal.)

And now 3D Systems has entered the chat.

Offering what it calls a "superior proposal" to all the other plans being floated, 3D proposed a cash-and-stock acquisition in which it pays $7.50 per share in cash and offers 1.2507 of its own shares in exchange for each share of Stratasys outstanding. In so doing, it would also create a $2 billion-plus-giant in the 3D printing industry.

Now what

Between the cash and shares, 3D's proposed buyout price is worth a hair over $19 a share -- so mathematically at least, it is a superior proposal. In addition, 3D notes that its plan would create a single "clear pure-play additive manufacturing leader with unmatched scale and [a] highly attractive financial profile."

Indeed, citing projected cost-saving synergies from the merger, 3D calculates that the actual value of its bid is closer to $25 a share (although how that math works is less clear, and to a large extent speculative). On top of all that, 3D is telling Stratasys shareholders that they can expect the combined company to grow its business at "approximately 21%" annually over the next five years -- and earn positive free cash flow of $121 million next year.

Will Stratasys's board of directors bite at this offer?

They might. Both Stratasys and 3D saw their sales shrink 9% in the most recent quarter. The prospect of reversing that trend and growing rapidly instead of shrinking has to sound especially attractive (even if it also sounds suspiciously optimistic). So far, however, all Stratasys has said in response to 3D's offer is that it will "carefully review" it  -- and that it's still planning to buy Desktop Metal in Q4 this year.  

Stay tuned.