4. Audax Health—Acquired by UnitedHealth Group
In February, Audax Health's 24-year-old CEO, Grant Verstanding, sold a majority stake in the company to UnitedHealth's Optum group. Terms of the deal weren't disclosed. Audax, which raised more than $55 million in funding, helps insurance companies and consumers create online health plans, and incentives to stick with them. It's a natural fit for the health insurance giant as it tries to improve technology and transparency.
5. MakerBot—Acquired by Stratasys
Together they're a 3-D printing behemoth. Stratasys, the leader in 3-D printing and manufacturing, paid $604 million for the leader in consumer and desktop printing, MakerBot. The June 2013 deal consisted of $403 million upfront in stock, plus incentives tied to MakerBot's performance in coming years.
Read More3 promising tech darlings that fell flat
6. Nest—Acquired by Google
For Google, thermostat maker Nest is the way into the connected home. In January it agreed to pay $3.2 billion for the company. Nest CEO Tony Fadell said the company will operate with some independence. There's no word yet on whether or when Google's software will be embedded into Nest devices. Nest did have one major snafu since the deal: Its new smoke alarm, Protect, had to be recalled for a fix when one of its signature features—motion recognition—was discovered capable of unintentionally disabling the device.
7. Tumblr—Acquired by Yahoo
Yahoo turned to Tumblr to snag a social platform, and the $1.1 billion deal last May raised concerns about overpaying for a company that had never turned a profit. Yahoo CEO Marissa Mayer said in her announcement of the deal: "We promise not to screw it up."
8. WhatsApp—Acquired by Facebook
How much is a text worth? A lot, judging from Facebook's biggest deal ever—$16 billion for the mobile messaging service. The February deal consists of $12 billion worth of Facebook shares and $4 billion in cash, plus an additional $3 billion in restricted stock units, which would vest over the next four years. The appeal? At the time of the deal, WhatsApp had 450 million users, and Facebook CEO Mark Zuckerberg said that number has the potential to grow to 1 billion.
Read MoreThe search for the Twitter of China
9. Waze—Acquired by Google
Google wants to win the mobile-mapping and navigation wars being waged against Apple and others, so it paid $1.1 billion for the crowd-sourced mobile mapping app, which uses input from its users—50 million at the time of the deal—to provide up-to-date traffic information. In purchasing Waze last June, Google eliminated a potential competitor and gained a leg up on Apple, as it attempts to improve its mobile mapping technology.