Given the market's dour mood early on, that the Dow Jones Industrials (INDEX: ^DJI) managed to eke out any gain at all is surprising. With concerns about earnings reports and a downbeat report from the housing sector, the Dow quickly lost 90 points. But as the day went on, it once again demonstrated its ability to bounce back from adversity.

What's even more surprising are the stocks that got it there. Microsoft (NASDAQ: MSFT) has been a highly unpopular stock for years, as the software giant has largely missed out on the massive run that more progressive technology companies have seen in their stocks over the past decade. But after a modest run-up to begin 2013, Microsoft's stock soared 3.6% today on news that activist investor ValueAct Capital had reported a $2 billion stake in the company. At this point, the move seems overblown, given that the position amounts to less than 1% of Microsoft's outstanding stock. But as a signal that investors may finally demand value-enhancing changes from the company, Microsoft should take the situation seriously.

The other surprise gainer was Caterpillar (NYSE: CAT), which some blamed for the Dow's initial drop after announcing disappointing earnings and guidance. Yet, by the end of the day, investors seemed to focus on the company's more upbeat statement of confidence and optimism about what it called the "relative stability" in the economies of the U.S. and China so far this year. That's hardly a glowing recommendation, given Caterpillar's guidance cut for 2013 earnings, but with the stock already having gotten beaten down, relieved investors bid shares up 2.8%.

Finally, outside the Dow, Power-One (NASDAQ: PWER) soared 57% after ABB (NYSE: ABB) made a $1 billion bid for the solar industry player. The ABB bid values Power-One at $6.35 per share, and the stock climbed to within just a couple of cents of that figure as investors take the acceptance of the deal as a foregone conclusion. Consolidation within the solar industry has been inevitable, and with Power-One's position in the solar inverter market, ABB hopes to bolster its sales by making Power-One's equipment available to the more than 100 countries in which ABB operates.

Do Caterpillar's gains today make sense given its long-term challenges, or is Caterpillar poised for further declines? Find out in the Motley Fool's premium research report, which highlights Caterpillar's solid competitive advantages. Just click here to access it now.

Fool contributor Dan Caplinger has no position in any stocks mentioned. You can follow him on Twitter @DanCaplinger. The Motley Fool owns shares of Microsoft and Power-One. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.