AltArc (Alternate Archive) was a user map archive run by Fraxtil.
- When registering, users may provide their Numa username which will provide others with a convenient link to their page on Numa.
- Protection against XSS attacks.
- Protection against brute-force login attempts, by requiring a CAPTCHA to be answered after 3 failed attempts.
- Sorting by rating, as well as number of votes, views, and favorites.
- Users can add maps to their favorites, as well as saving maps, which adds them to a separate list that has no effect on the map's popularity.
- Filtering maps by title, type, author, class (generalized type such as playable and nonplayable).
- The front page is a list of the top-rated maps in the past 24 hours.
- Collaborative levels: one user can submit a collaborative map, send another user a secret code, and have the other user enter that code in order to add the user to the authors.
- The default theme was designed by incluye and coded by Gforce, incluye, and sidke.
- Multiple demos (four maximum) may be submitted in one comment. Demos prefixed with "[AGD]" are more visually evident.
- Map packs are supported (they behave like map types), and users are able to download entire packs in userlevels.txt format.
- Users may append messages to their comments, but cannot completely re-write or delete them.
- Sorting by number of comments.
- Users may design visual styles for the site and upload them so anyone may use the stylesheets.
- Comments may be sorted by newest (default) or oldest, according to a user's preference.
- Users will be able to batch-download any group of maps based upon search results, without truncation.