The Company maintains a stock-based compensation plan, the 2011 Incentive Compensation Plan, as amended, (the “2011 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.

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 grant under the 2011 Plan, including shares rolled over from the 2007 Plan and the 2010 Plan. Subsequent to June 6, 2011 through March 31, 2021, the number of shares of common stock authorized for issuance under the 2011 Plan has been increased by an aggregate of 4,400,000 shares.

A summary of activity for the Company’s stock option plans for the three months ended March 31, 2021 is as follows:

	Number Outstanding			Average Exercise Price per Share		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balance at December 31, 2020		550,769		$	5.56		4.88	$	1,875,719
Granted		—			—
Cancelled or Expired		(292	)		14.40
Exercised		(5,254	)		6.50
Balance at March 31, 2021		545,223		$	5.53		4.68	$	3,318,621
Vested or expected to vest at March 31, 2021		545,223		$	5.53		4.68	$	3,318,621
Exercisable at March 31, 2021		545,223		$	5.53		4.68	$	3,318,621

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 March 31, 2021:

	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		458,510		5.09	$	4.43		458,510	$	4.43
$7.50 - $11.25		66,544		2.94		10.04		66,544		10.04
$11.30 - $16.95		13,472		1.43		12.86		13,472		12.86
$17.60 - $26.40		6,697		0.49		21.55		6,697		21.55
$4.36 - $26.40		545,223		4.68	$	5.53		545,223	$	5.53

As of March 31, 2021, there was no unrecognized stock-based compensation expense related to stock options.

The following is a summary of RSU activity for the three months ended March 31, 2021:

	Number Outstanding			Weighted Average Fair Value
Unvested at December 31, 2020		682,563		$	4.34
Granted		82,151			11.18
Vested		(124,558	)		5.32
Forfeited		(7,063	)		2.93
Unvested at March 31, 2021		633,093		$	5.05
Shares vested but not released		344,726		$	5.08

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 March 31, 2021, there was $2.6 million of unrecognized compensation expense related to unvested RSUs granted, which is expected to be recognized over a weighted average period of 2.5 years.

The Company granted 200,000 PSUs to a certain key employee during the year ended December 31, 2020, with a grant date fair value of $6.38 per share. The PSUs are subject to the attainment of performance goals established by the Company’s Compensation Committee, the periods during which performance is to be measured, and other limitations and conditions. Performance goals are based on pre-established objectives that specify the manner of determining the number of PSUs that will vest if performance goals are attained. If the employee terminates employment, the non-vested portion of the PSUs will not vest and all rights to the non-vested portion will terminate.

The following is a summary of PSU activity for the three months ended March 31, 2021:

	Number Outstanding
Unvested at December 31, 2020		200,000
Granted		—
Vested		(20,000	)
Forfeited		—
Unvested at March 31, 2021		180,000

As of March 31, 2021, there was $1.1 million of unrecognized compensation cost related to unvested PSUs, which is expected to be recognized over a period of 1.8 years. No tax benefit was realized from PSUs for the three months ended March 31, 2021.

The following table summarizes stock-based compensation expense related to stock options, RSUs, and PSUs included in the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2021 and 2020 (in thousands):

	Three Months Ended March 31,
	2021		2020
Cost of revenue	$	33	$	40
Research and development		162		174
Selling and marketing		103		126
General and administrative		460		300
Total	$	758	$	640

During the three months ended March 31, 2021 and 2020, the Company repurchased 25,327 and 48,335 shares, respectively, of common stock surrendered to the Company to satisfy tax withholding obligations in connection with the vesting of RSUs issued to employees.