Harmonic weak Maas forms have recently been shown to have quite a few interesting arithmetic applications, including their connection to Ramanujan’s work on (mock) theta functions (Bringmann and Ono in Invent. Math. 165(2):243–266, 2006; Bringmann and Ono in Ann. Math. 171(1):419–449, 2010; Bruinier and Ono in Heegner divisors, L-functions and harmonic weak Maass forms, Ann. Math., 2011, to appear; Zagier in Ramanujan’s mock theta functions and their applications [d’apres Zwegers and Bringmann–Ono] Seminaire Bourbaki 986, 2006–2007).