The Company has a stock-based compensation plan to attract, motivate, retain and reward employees, directors and consultants by providing its Board or a committee of the Board the discretion to award equity incentives to these persons. The Company’s stock-based compensation plan consists of the 2011 Incentive Compensation Plan (the “2011 Plan”), as amended. Shares are no longer available for issuance under the Company’s 2010 Bonus and Incentive Plan (the “2010 Plan”) and the 2007 Stock Option Plan (the “2007 Plan”).

On June 6, 2011, the Company’s stockholders approved the 2011 Plan, which is administered by the Compensation Committee of the Board. The 2011 Plan provides that stock options, stock units, restricted shares, and stock appreciation rights may be granted to executive officers, directors, consultants, and other key employees. The Company reserved 400,000 shares of common stock under the 2011 Plan, plus 459,956 shares of common stock that remained available for delivery under the 2007 Plan and the 2010 Plan as of June 6, 2011. In aggregate, as of June 6, 2011, 859,956 shares were available for future grants under the 2011 Plan, including shares rolled over from the 2007 Plan and the 2010 Plan. Subsequent to June 6, 2011 through December 31, 2017, the number of shares of common stock authorized for issuance under the 2011 Plan has been increased by an aggregate of 3,000,000 shares. On May 31, 2018, the Company’s stockholders approved an amendment to the 2011 Plan to increase the number of shares of common stock authorized for issuance by 500,000 shares.

A summary of activity for the Company’s stock option plans for the six months ended June 30, 2019 follows:

	Number Outstanding			Average Exercise Price per Share		Weighted Average Remaining Contractual Term (Years)		Average Intrinsic Value
Balance at December 31, 2018		621,602		$	5.87		6.32	$	—
Granted		—			—
Cancelled or Expired		(46,000	)		8.52
Exercised		—			—
Balance at June 30, 2019		575,602		$	5.66		6.32	$	337,790
Vested or expected to vest at June 30, 2019		575,387		$	5.66		6.32	$	337,627
Exercisable at June 30, 2019		547,823		$	5.72		6.28	$	316,678

The aggregate intrinsic value in the table above represents the difference between the fair value of the Company’s common stock and the option exercise price of in-the-money options multiplied by the number of such options.

The following table summarizes information about options outstanding as of June 30, 2019:

	Options Outstanding						Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$4.36 - $7.20		468,810		6.78	$	4.46		441,031	$	4.46
$7.50 - $11.30		85,198		4.64		9.74		85,198		9.74
$12.00 - $19.70		17,244		3.01		13.60		17,244		13.60
$21.70 - $24.20		4,350		2.18		23.27		4,350		23.27
$4.36 - $24.20		575,602						547,823

At June 30, 2019, there was $0.06 million of unrecognized stock-based compensation expense, net of estimated forfeitures related to unvested options, that is expected to be recognized over a weighted-average period of 0.19 years.

The following is a summary of RSU activity for the six months ended June 30, 2019:

	Number of RSUs			Weighted Average Fair Value
Unvested at December 31, 2018		1,367,630		$	3.81
Granted		289,500			5.21
Vested		(354,669	)		3.53
Forfeited		(27,582	)		3.98
Unvested at June 30, 2019		1,274,879		$	4.19
Shares vested but not released		171,850		$	5.38

The fair value of the Company’s RSUs is calculated based upon the fair market value of the Company’s stock on the date of grant. As of June 30, 2019, there was $4.4 million of unrecognized compensation expense related to unvested RSUs granted, which is expected to be recognized over a weighted average period of 2.8 years.

The following table illustrates all employee stock-based compensation expense related to stock options and RSUs included in the condensed consolidated statements of operations for the three and six months ended June 30, 2019 and 2018 (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Cost of revenue	$	34	$	22	$	63	$	41
Research and development		113		136		227		271
Selling and marketing		205		189		385		348
General and administrative		341		301		705		624
Total	$	693	$	648	$	1,380	$	1,284

During the six months ended June 30, 2019 and 2018, the Company repurchased 98,939 and 71,635 shares, respectively, of common stock surrendered to the Company to satisfy tax withholding obligations in connection with the vesting of RSUs issued to employees.