This is a list of my favorite artificial (non-magical) heroines.  The reason I thought this up was because I am currently replaying Komorebi no Nostalgica, which is pretty much the top for an AI-focused VN.  

Emmy from Akabanzu  https://vndb.org/c42670

Akabanzu itself is an unusual game in that it is a charage focused on a protagonist being forcibly rehabilitated from game addiction.  The AI in this game, Emmy, focuses on a support role, which makes for a surprisingly interesting (and comedic) story.  She isn't one of my absolute favorites, but failing to note her would leave the ignorant with no way to know such a VN existed.

Tsukuyomi from Kamikimi  https://vndb.org/c85636

Tsukuyomi is a pretty interesting individual AI.  Designed from the beginning to answer the protagonist's desires, she is somewhat... excessively enthusiastic about what she considers to be her duties.  However, her story as a heroine and a side-character in the other routes is powerful, so I honestly consider her a good choice for a robot waifu.

Himefuuro from Missing X-link  https://vndb.org/c78927

Himefuuro is an AI designed to form empathic links with her master, one of two projects (the other conflict-oriented).  I'll be straight and say she is a lot like a cross between an older sister who spoils her younger brother rotten, a psychological therapist, and a maid.  Her role is rather unusual while at the same time being the epitome of what a young male with a scarred psyche would seek from an empathic AI.

Accela from Reminiscence  https://vndb.org/c12819

In the underground arcology that Reminiscence is based in, robots like Accela serve a number of service roles, and they have evolved a great deal since the age of Akagoei (which was centuries before).  However, Accela is unusual in that her limiters (especially on emotional reactions) have been removed.  She is the glue that keeps Aki and Hidetaka from breaking into pieces, a dear friend to Aki, and the holder of an emotional debt he won't even allow himself to speak of to Hidetaka.  

Fluorite Alvega of Komorebi no Nostalgica  https://vndb.org/c11680

A member of a race of self-aware and independent AIs in the twenty-fifth century, she is straight-out a member of the 'group of friends' in the game, having grown up with them quite literally.  She is still in the process of developing emotionally (a process that never really ends, apparently), and her mechanical origins are obvious by her choice of wording and mannerisms.  However, she does display emotion (if subtly) and cares about her friends (and Shouta in particular) greatly.  As the member of a publicly-acknowledged machine race with equal rights to humans, she is unique on this list.

Neueblau T MILLA of Re:Birth Colony  https://vndb.org/c44998

An AI 'child' born of the genius of a single scientist and grown inside a partially biological body, she is unusual on this list that while her origins are entirely artificial, she is nonetheless partially biological.  She is an agent and diplomat for another arcology, and she acts as such, partly out of her duty to search out and handle dangers born of pre-Disaster projects.  As a lover, there is little difference between her and the average human, save that she can switch bodies at need.  Her older sister is married to the protagonist of Fake Azure Arcology in the story's canon and is also an AI.

Misora of Shiawase Kazoku-bu  https://vndb.org/c23258

What can I say about Misora?  Think 'standard-issue anime robot heroine' and you won't be far off.  The game itself is more notable than her, similar to Akabanzu.

Ripple of Aekanaru Sekai no Owari ni  https://vndb.org/c58825

The mischievous AI main character and main heroine of the sci-fi VN Aekanaru Sekai no Owari ni.  I could say a lot about her, but not without spoiling the game.  The game gets mixed reviews from those who like this kind of thing (mostly because of its age), but Ripple is a pretty good AI heroine, if one that is less 'convenient' as a heroine than most (you'll understand what I mean if you play the game).  

 

There are other AI heroines out there (many of whom I have probably forgotten or don't consider to be heroines) but these are the ones that came to mind when I asked myself about AI heroines from games I could feel safe recommending.