Because ἁπτομαι is much more common in usage, beginners often learn this form first and are tempted to assume that it is a deponent.
In recent years, there has been a sustained challenge to the notion of deponency by scholars of ancient Greek.
Their form (except in the present and future participle) is that of a passive verb, but the meaning is active.
Examples are hortārī ('to exhort'), verērī ('to fear'), loquī ('to speak'), blandīrī ('to flatter'), and many more.
Old Irish has a substantial number of deponent verbs, some of them very common, such as do·muinethar 'think, suppose' and cuirethar 'put'.
The pattern was not continued into the modern languages and all such verbforms were ultimately replaced by 'normal' forms.
As the passive is a secondary formation (based on a different stem with middle endings), all deponent verbs take middle-voice forms, such as सच॑ते sác-ate.
Swedish has a few passive-voice deponents, although its closely related neighbour languages Danish and Norwegian mostly use active corresponding forms.
Indeed, Norwegian shows the opposite trend: like in English, active verbs are sometimes used with a passive or middle sense, such as in boka solgte 1000 eksemplarer 'the book sold 1000 copies'.
A handful of Swedish deponent verbs are specifically used for reciprocal or continuous meanings.
Latin has a few semi-deponent verbs, which have active forms in the present, future, and imperfect tenses, but are deponent in the perfect system.