Here are the closed questions tagged (at this date) with the deprecated abstract-algebra.
finite index, self-normalizing subgroup of $F_2$
https://mathoverflow.net/questions/47534/unit-ideal-in-non-commutative-rings
https://mathoverflow.net/questions/157122/algebra-generated-by-a-tree-edit
Why do we not lose any generality by proving it only for finitely generated groups
https://mathoverflow.net/questions/225240/group-associated-to-the-monoid-cal-px-times-x-circ
Making idempotent element by a relation
How to solve this system of equations?
https://mathoverflow.net/questions/127611/an-exercise-about-tor
Is the "algebraic closure" of the quaternions, finite dimensional?
https://mathoverflow.net/questions/266080/does-alexander-whitney-formula-imply-pythagoras-theorem
Is there any construction of infinite dimensional algebraic division ring?
Polynomial constraints triggered by irreducibility
Does this solution guarantee $det(A)=0$ where $A\in M(R)$?
Is $K\cap \langle H\cup N\rangle\subseteq \langle H\cup (K\cap N)\rangle$?