ている

1. 1An action that is currently in progress ('is doing').Ex. 1
2. 2A state that continues after a change has taken place ('is married', 'is open').Ex. 2
3. 3A habitual or repeated action, such as a job or routine ('works at', 'goes every day').

A very common, neutral pattern used in everyday speech and writing, with ています in polite contexts and the contracted てる in casual talk. Whether it means 'in progress' or 'resulting state' depends largely on the verb: action verbs like 作る usually give a progressive meaning, while change-of-state verbs like 結婚する or 死ぬ give a resulting-state meaning.

• てあるN4「てある」 takes only transitive verbs and overlaps with 「ている」 only in the resulting-state sense, but it implies that someone did it deliberately or prepared it in advance. 「窓が開けてある」 suggests someone opened the window, whereas 「窓が開いている」 just describes its state.
• ているところN4「ているところ」 matches only the ongoing-action sense, stressing that the action is underway at that very moment, and often appears with 「今」 or 「ちょうど」. It can't replace 「ている」 for resulting states or habitual or repeated actions, nor with stative verbs like 「いる」 and 「知る」.
• つつあるN2「つつある」 attaches to the ます-stem, is formal, and takes only change verbs, stressing that a change is gradually progressing and not yet complete. Unlike 「ている」, it can't express simple ongoing action, resulting state, or habit, so 「食べつつある」 is not said.
• たばかりN4「たばかり」 attaches to the た-form and means shortly after an action is completed or a new state begins, with a subjective 'only just' feel, whereas 「ている」 in its resulting-state sense only says the state continues, regardless of how long. 「結婚している」 means 'married', while 「結婚したばかり」 means 'newlywed'.
• っぱなしN3「っぱなし」 attaches to the ます-stem, is colloquial, and describes leaving something as it is when it should have been dealt with, or continuing the same action for a long time, often with displeasure. 「ている」 attaches to the て-form and objectively states ongoing, resulting, or habitual situations without any judgment.
• 中N3The two overlap only in the 'currently in progress' sense: 「中」, read 「ちゅう」, follows action nouns like 「会議中」 and is common on notices and in phone responses, while 「ている」 follows the て-form of verbs. 「中」 can also mean 'throughout' and 'within'.

ている broadly marks an ongoing action or resulting state, while てある stresses a state left by someone's deliberate action and ているところ pinpoints being right in the middle of an action. つつある marks a gradual change underway, たばかり stresses that something has just happened, っぱなし implies something left in a state (often negatively), and 中 attaches to nouns (会議中) to mean 'in the middle of'.