DALsys/DALsystems is the claimed signature from a modeler/texture artist on the BM development team, Brian Dale (a.k.a. bkdale86), as he revealed in a thread he made in the "Developer Updates" section on the forums in early March, 2014.  
In the game, the DALsys/DALsystems "brand name" can be seen on various items and assets throughout the Black Mesa Research Facility, such as:
- A wall-mounted computer terminal in the lobby of Sector C Test Labs.
- Various mainframe/server computers.
- Various lab/engineering/security consoles.
- Copy machines (found in various offices including one in the Biodome Complex Administration Offices, and one in Dr. Horn's office).
- A wall console (possibly a videophone) in Dr. Horn's office, with a numeric keypad and a display screen showing a login prompt and the logos of the US Department of Energy and the BMRF in the background.
- Telecommunication systems inside the HEV suit boot sequence.
Some of the consoles have numeric LED displays displaying various numbers. Thus far, none of these numbers have been proven to be linked to the ARG.
DALsys employees loginEdit
On the BMRF website, which appeared around November 5, 2013, a link titled "DALsys employees login" leads to a web page at terminal.bmrf.us which is displaying a DALsystems remote terminal login screen.
Early in course of the ARG, forum users discovered an internet domain named dalsystems.com. A whois lookup of the domain did not reveal the owner of the domain since the domain was registered through an anonymization service. At the time, nothing of interest was found on the site hosted on the domain, and the domain and site was eventually dismissed as a dead end.
After the appearance of the BMRF site around November 5, 2013, followed by the (inactive) DALsystems remote terminal login screen on November 7, 2013, one forum user revisited the dalsystems.com site and discovered that the site had changed since it was last discussed on the forum.
On the top right of the page, there was a login button which opened up a login prompt requiring a username and a password. The login prompt also had a password retrieval option. Attempts to use this function would only display the message "Retrieve Password option is currently unavailable."
The example companies, organizations, products, people and events depicted herein are fictitious. No association with any real company, organization, product, person, or event is intended or should be inferred.
On February 25, 2014, it was noted by an anonymous wiki user that the http://www.dalsystems.com/ website redirected to a login screen at Microsoft Office 365.
Further investigation showed that the domain was now set up to use a URL redirection service which redirected to https://dalsystems.sharepoint.com/, which in turn redirected to the Office 365 login page.
A day or two later, the destination URL was changed to https://dalsystems-public.sharepoint.com/ which (as of February 27, 2014) was displaying a template Microsoft SharePoint Online Public Website (part of the Office 365 suite). http://dalsystems.com/ (without the www) was however still redirecting to https://dalsystems.sharepoint.com/.
On November 22, 2014, a routine visit to the site revealed that the site had changed yet again. http://www.dalsystems.com/ was now redirecting to https://dalsystems.azurewebsites.net/. Another whois lookup of the dalsystems.com domain was done. Now, the Whois Record revealed the true owner of the dalsystems.com domain, who was previously hidden. However, it turned out that the owner/registrant was not Brian Dale (bkdale86) or any of the other developers.
Given the most recent evidence, it appears that the dalsystems.com site is not in any way related to Brian Dale, Black Mesa or the ARG, except in name only.