I posted an Avengers/Doctor Who crossover fic! It is here:
Keep Your Knees Bent; Roll With It (Or: Darcy's Job Situation Is Complicated
It is based on a prompt about Darcy being an ex-Companion, and how S.H.I.E.L.D. and U.N.I.T. both want to employ her. (But my fic itself is mostly about Darcy finding a place to fit in. Plus: drinks with River.)
It is G, and has no pairings (except implied Doctor/River)!