Offloads some basic brain functions to a remote server, allowing the host to focus on more pressing matters.
Net Downlink is an augment which gives the agent +2 AP whenever all firewalls are broken on a mainframe device, up to a maximum of +6 AP per turn. It is not possible to install more than one Net Downlink on the same agent.
Net Downlink is considered to be one of the best augments in the game. It is not the only augment that can give a bonus of up to +6 AP per turn, but its bonus can be triggered more often than other augments — it is usually more common to hack multiple devices per turn, than it is to make melee attacks (for Predictive Brawling's bonus) or to cloak (for Chameleon Movement's bonus).
When playing with Net Downlink, it is often a good idea to hack a device for no other reason than to get the AP bonus — and even to explore more of the facility so you have more opportunities to use Net Downlink. For example, you can hack Sound Bugs even if you have no intention of making noise near them; or peek through a Vault Door even if you don't have a Vault Access Card, simply so you can hack a device behind it.
If there are many devices to hack, it can be best to avoid hacking more than 3 per turn to avoid wasting the bonus; take particular care when using Data Blast in a dense area, to leave some devices for later turns. You may sometimes also plan to leave a device deliberately unhacked so that Net Downlink can be used in an emergency, similar in purpose to a Stim. The bonus from Net Downlink is particularly useful when you need to sprint but don't have quite enough AP to start sprinting.
The fact that Net Downlink exists is reason enough to avoid installing lower-value augments such as Skeletal Suspension or Titanium Rods too early in a campaign — augment sockets are limited, so it is often better to have a spare socket available in case you find Net Downlink later. If you don't have any spare sockets, consider taking Net Downlink into the final mission to install on Central or Monst3r; or in Endless mode, you can use an Augment Drill to remove a different augment and replace it with Net Downlink.