The 30-year-old put pen-to-paper on Friday afternoon to link up with the Pilgrims and is eligible to make his debut against Colwyn Bay on Saturday.
Foster was part of the all-conquering Eastwood Town side which won the UniBond Premier League and enjoyed tremendous FA Cup success in 2008-2009.
In addition to his successful spell with Eastwood, Foster has Blue Square Bet North experience with FC Halifax Town.
Manager Graham Drury told bufc.co.uk: “The existing players have had five matches to impress and our results, in the main, are still the same.
“Therefore, I need to start introducing more new players into the squad and Anton is a welcome addition.
“He will add bite and experience to the midfield and he is a player that I have admired for a long time.”
Foster has also previously played for the likes of Buxton, Belper Town and Gedling Town.