Sentence finishing by "interested", is Ok or should end by "in" or "by"?

Solution 1:

I would rephrase as follows: 'This demo application contains features which might be of interest to you.'

Solution 2:

Go ahead and use "in". If Shakespeare could end a sentence with a preposition, then so can we!

Solution 3:

INTERESTED is an adjective. We become" interested in something". Your sentence without the preposition IN becomes two separate clauses. We write the sentence the other way round to make it obvious.

• This demo application contains features (in which) you may be interested.

When we elide WHICH it becomes necessary to place IN at the rear with INTERSET it is related to. Here my foregoing sentence has been construed in the same way. Grammarly is correct in using IN.